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 $24.73   5.272%   $26.0338   $26.03   $26.05   $26.00  
  Purchase #2 $114.64   12.827%   $129.3449   $129.34   $129.35   $129.30  
  Purchase #3 $55.33   8.338%   $59.9434   $59.94   $59.95   $59.90  
  Purchase #4 $102.88   9.338%   $112.4869   $112.49   $112.50   $112.50  
  Purchase #5 $151.71   4.703%   $158.8449   $158.84   $158.85   $158.80  
  Purchase #6 $72.48   12.287%   $81.3856   $81.39   $81.40   $81.40  
  Purchase #7 $178.87   5.830%   $189.2981   $189.30   $189.30   $189.30  
  7 purchase totals = $700.64       $757.3376   $757.33   $757.40   $757.20