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 $53.94   5.719%   $57.0248   $57.02   $57.00   $57.00  
  Purchase #2 $130.57   7.503%   $140.3667   $140.37   $140.35   $140.40  
  Purchase #3 $215.38   4.290%   $224.6198   $224.62   $224.60   $224.60  
  Purchase #4 $37.62   3.655%   $38.995   $39.00   $39.00   $39.00  
  Purchase #5 $61.56   10.781%   $68.1968   $68.20   $68.20   $68.20  
  Purchase #6 $146.37   5.484%   $154.3969   $154.40   $154.40   $154.40  
  Purchase #7 $177.41   10.143%   $195.4047   $195.40   $195.40   $195.40  
  7 purchase totals = $822.85       $879.0047   $879.01   $878.95   $879.00