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 $51.62   12.873%   $58.265   $58.27   $58.25   $58.30  
  Purchase #2 $115.66   3.439%   $119.6375   $119.64   $119.65   $119.60  
  Purchase #3 $37.46   5.203%   $39.409   $39.41   $39.40   $39.40  
  Purchase #4 $196.75   10.653%   $217.7098   $217.71   $217.70   $217.70  
  Purchase #5 $239.84   6.556%   $255.5639   $255.56   $255.55   $255.60  
  Purchase #6 $162.76   12.610%   $183.284   $183.28   $183.30   $183.30  
  Purchase #7 $86.92   5.428%   $91.638   $91.64   $91.65   $91.60  
  7 purchase totals = $891.01       $965.5072   $965.51   $965.50   $965.50