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 $136.32   11.702%   $152.2722   $152.27   $152.25   $152.30  
  Purchase #2 $126.95   9.498%   $139.0077   $139.01   $139.00   $139.00  
  Purchase #3 $69.56   7.557%   $74.8166   $74.82   $74.80   $74.80  
  Purchase #4 $112.97   9.105%   $123.2559   $123.26   $123.25   $123.30  
  Purchase #5 $8.94   11.226%   $9.9436   $9.94   $9.95   $9.90  
  Purchase #6 $51.95   4.355%   $54.2124   $54.21   $54.20   $54.20  
  Purchase #7 $246.56   4.800%   $258.3949   $258.39   $258.40   $258.40  
  7 purchase totals = $753.25       $811.9033   $811.90   $811.85   $811.90