Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.71   13.742%   $236.2535   $236.25   $236.25   $236.30  
  Purchase #2 $110.87   12.701%   $124.9516   $124.95   $124.95   $125.00  
  Purchase #3 $183.31   5.116%   $192.6881   $192.69   $192.70   $192.70  
  Purchase #4 $214.25   11.751%   $239.4265   $239.43   $239.45   $239.40  
  Purchase #5 $183.65   13.632%   $208.6852   $208.69   $208.70   $208.70  
  Purchase #6 $198.55   6.765%   $211.9819   $211.98   $212.00   $212.00  
  Purchase #7 $179.28   12.743%   $202.1257   $202.13   $202.15   $202.10  
  7 purchase totals = $1,277.62       $1,416.1125   $1,416.12   $1,416.20   $1,416.20