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 $94.77   10.278%   $104.5105   $104.51   $104.50   $104.50  
  Purchase #2 $88.92   5.192%   $93.5367   $93.54   $93.55   $93.50  
  Purchase #3 $116.53   11.106%   $129.4718   $129.47   $129.45   $129.50  
  Purchase #4 $101.63   6.726%   $108.4656   $108.47   $108.45   $108.50  
  Purchase #5 $43.82   5.740%   $46.3353   $46.34   $46.35   $46.30  
  Purchase #6 $125.85   8.573%   $136.6391   $136.64   $136.65   $136.60  
  Purchase #7 $51.46   11.508%   $57.382   $57.38   $57.40   $57.40  
  7 purchase totals = $622.98       $676.3410   $676.35   $676.35   $676.30