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 $132.63   13.617%   $150.6902   $150.69   $150.70   $150.70  
  Purchase #2 $15.58   11.494%   $17.3708   $17.37   $17.35   $17.40  
  Purchase #3 $175.98   7.256%   $188.7491   $188.75   $188.75   $188.70  
  Purchase #4 $58.40   4.402%   $60.9708   $60.97   $60.95   $61.00  
  Purchase #5 $72.53   6.836%   $77.4882   $77.49   $77.50   $77.50  
  Purchase #6 $58.75   12.522%   $66.1067   $66.11   $66.10   $66.10  
  Purchase #7 $45.62   11.344%   $50.7951   $50.80   $50.80   $50.80  
  7 purchase totals = $559.49       $612.1709   $612.18   $612.15   $612.20