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 $29.60   10.590%   $32.7346   $32.73   $32.75   $32.70  
  Purchase #2 $221.54   9.147%   $241.8043   $241.80   $241.80   $241.80  
  Purchase #3 $110.66   13.146%   $125.2074   $125.21   $125.20   $125.20  
  Purchase #4 $159.28   11.296%   $177.2723   $177.27   $177.25   $177.30  
  Purchase #5 $59.66   13.138%   $67.4981   $67.50   $67.50   $67.50  
  Purchase #6 $190.59   12.143%   $213.7333   $213.73   $213.75   $213.70  
  Purchase #7 $178.53   9.284%   $195.1047   $195.10   $195.10   $195.10  
  7 purchase totals = $949.86       $1,053.3547   $1,053.34   $1,053.35   $1,053.30