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 $57.97   7.204%   $62.1462   $62.15   $62.15   $62.10  
  Purchase #2 $137.89   13.658%   $156.723   $156.72   $156.70   $156.70  
  Purchase #3 $207.95   6.480%   $221.4252   $221.43   $221.45   $221.40  
  Purchase #4 $234.28   6.607%   $249.7589   $249.76   $249.75   $249.80  
  Purchase #5 $45.87   4.672%   $48.013   $48.01   $48.00   $48.00  
  Purchase #6 $7.53   11.233%   $8.3758   $8.38   $8.40   $8.40  
  Purchase #7 $53.71   6.152%   $57.0142   $57.01   $57.00   $57.00  
  7 purchase totals = $745.20       $803.4563   $803.46   $803.45   $803.40