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 $207.46   4.124%   $216.0157   $216.02   $216.00   $216.00  
  Purchase #2 $238.40   8.341%   $258.2849   $258.28   $258.30   $258.30  
  Purchase #3 $207.98   7.833%   $224.2711   $224.27   $224.25   $224.30  
  Purchase #4 $41.27   7.805%   $44.4911   $44.49   $44.50   $44.50  
  Purchase #5 $156.60   10.255%   $172.6593   $172.66   $172.65   $172.70  
  Purchase #6 $176.62   12.134%   $198.0511   $198.05   $198.05   $198.10  
  Purchase #7 $107.55   11.275%   $119.6763   $119.68   $119.70   $119.70  
  7 purchase totals = $1,135.88       $1,233.4495   $1,233.45   $1,233.45   $1,233.60