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 $84.35   11.429%   $93.9904   $93.99   $94.00   $94.00  
  Purchase #2 $62.45   8.700%   $67.8832   $67.88   $67.90   $67.90  
  Purchase #3 $250.51   4.170%   $260.9563   $260.96   $260.95   $261.00  
  Purchase #4 $165.38   11.417%   $184.2614   $184.26   $184.25   $184.30  
  Purchase #5 $200.68   6.141%   $213.0038   $213.00   $213.00   $213.00  
  Purchase #6 $92.60   13.323%   $104.9371   $104.94   $104.95   $104.90  
  Purchase #7 $26.94   9.232%   $29.4271   $29.43   $29.45   $29.40  
  7 purchase totals = $882.91       $954.4593   $954.46   $954.50   $954.50