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 $92.78   12.631%   $104.499   $104.50   $104.50   $104.50  
  Purchase #2 $93.61   12.114%   $104.9499   $104.95   $104.95   $104.90  
  Purchase #3 $89.30   12.231%   $100.2223   $100.22   $100.20   $100.20  
  Purchase #4 $68.48   10.334%   $75.5567   $75.56   $75.55   $75.60  
  Purchase #5 $73.97   3.149%   $76.2993   $76.30   $76.30   $76.30  
  Purchase #6 $120.41   4.625%   $125.979   $125.98   $126.00   $126.00  
  Purchase #7 $170.54   13.732%   $193.9586   $193.96   $193.95   $194.00  
  7 purchase totals = $709.09       $781.4648   $781.47   $781.45   $781.50