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 $44.58   12.177%   $50.0085   $50.01   $50.00   $50.00  
  Purchase #2 $247.38   6.838%   $264.2958   $264.30   $264.30   $264.30  
  Purchase #3 $154.66   7.864%   $166.8225   $166.82   $166.80   $166.80  
  Purchase #4 $118.39   8.770%   $128.7728   $128.77   $128.75   $128.80  
  Purchase #5 $14.70   5.568%   $15.5185   $15.52   $15.50   $15.50  
  Purchase #6 $58.25   6.748%   $62.1807   $62.18   $62.20   $62.20  
  Purchase #7 $111.42   10.517%   $123.138   $123.14   $123.15   $123.10  
  7 purchase totals = $749.38       $810.7368   $810.74   $810.70   $810.70