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 $36.51   7.326%   $39.1847   $39.18   $39.20   $39.20  
  Purchase #2 $217.42   11.104%   $241.5623   $241.56   $241.55   $241.60  
  Purchase #3 $195.92   10.622%   $216.7306   $216.73   $216.75   $216.70  
  Purchase #4 $91.81   10.123%   $101.1039   $101.10   $101.10   $101.10  
  Purchase #5 $197.54   6.300%   $209.985   $209.99   $210.00   $210.00  
  Purchase #6 $232.89   12.266%   $261.4563   $261.46   $261.45   $261.50  
  Purchase #7 $6.64   3.855%   $6.896   $6.90   $6.90   $6.90  
  7 purchase totals = $978.73       $1,076.9188   $1,076.92   $1,076.95   $1,077.00