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 $20.50   7.193%   $21.9746   $21.97   $21.95   $22.00  
  Purchase #2 $210.78   5.213%   $221.768   $221.77   $221.75   $221.80  
  Purchase #3 $154.88   12.188%   $173.7568   $173.76   $173.75   $173.80  
  Purchase #4 $75.42   7.510%   $81.084   $81.08   $81.10   $81.10  
  Purchase #5 $98.32   11.355%   $109.4842   $109.48   $109.50   $109.50  
  Purchase #6 $122.80   7.751%   $132.3182   $132.32   $132.30   $132.30  
  Purchase #7 $180.46   4.239%   $188.1097   $188.11   $188.10   $188.10  
  7 purchase totals = $863.16       $928.4955   $928.49   $928.45   $928.60