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 $77.54   8.297%   $83.9735   $83.97   $83.95   $84.00  
  Purchase #2 $155.64   9.294%   $170.1052   $170.11   $170.10   $170.10  
  Purchase #3 $218.53   11.149%   $242.8939   $242.89   $242.90   $242.90  
  Purchase #4 $5.37   4.194%   $5.5952   $5.60   $5.60   $5.60  
  Purchase #5 $196.62   9.791%   $215.8711   $215.87   $215.85   $215.90  
  Purchase #6 $212.98   11.143%   $236.7124   $236.71   $236.70   $236.70  
  Purchase #7 $94.27   6.490%   $100.3881   $100.39   $100.40   $100.40  
  7 purchase totals = $960.95       $1,055.5394   $1,055.54   $1,055.50   $1,055.60