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 $55.75   7.133%   $59.7266   $59.73   $59.75   $59.70  
  Purchase #2 $203.72   4.237%   $212.3516   $212.35   $212.35   $212.40  
  Purchase #3 $208.97   3.367%   $216.006   $216.01   $216.00   $216.00  
  Purchase #4 $51.38   7.649%   $55.3101   $55.31   $55.30   $55.30  
  Purchase #5 $125.44   7.808%   $135.2344   $135.23   $135.25   $135.20  
  Purchase #6 $26.46   6.233%   $28.1093   $28.11   $28.10   $28.10  
  Purchase #7 $151.60   4.580%   $158.5433   $158.54   $158.55   $158.50  
  7 purchase totals = $823.32       $865.2813   $865.28   $865.30   $865.20