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 $182.50   8.153%   $197.3792   $197.38   $197.40   $197.40  
  Purchase #2 $115.47   3.125%   $119.0784   $119.08   $119.10   $119.10  
  Purchase #3 $189.89   10.638%   $210.0905   $210.09   $210.10   $210.10  
  Purchase #4 $28.47   9.593%   $31.2011   $31.20   $31.20   $31.20  
  Purchase #5 $139.95   6.484%   $149.0244   $149.02   $149.00   $149.00  
  Purchase #6 $136.90   9.801%   $150.3176   $150.32   $150.30   $150.30  
  Purchase #7 $74.60   10.539%   $82.4621   $82.46   $82.45   $82.50  
  7 purchase totals = $867.78       $939.5533   $939.55   $939.55   $939.60