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 $57.77   11.788%   $64.5799   $64.58   $64.60   $64.60  
  Purchase #2 $158.82   11.419%   $176.9557   $176.96   $176.95   $177.00  
  Purchase #3 $122.31   7.553%   $131.5481   $131.55   $131.55   $131.50  
  Purchase #4 $13.50   5.584%   $14.2538   $14.25   $14.25   $14.30  
  Purchase #5 $139.95   6.208%   $148.6381   $148.64   $148.65   $148.60  
  Purchase #6 $213.36   9.226%   $233.0446   $233.04   $233.05   $233.00  
  Purchase #7 $149.49   7.227%   $160.2936   $160.29   $160.30   $160.30  
  7 purchase totals = $855.20       $929.3138   $929.31   $929.35   $929.30