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 $24.80   13.804%   $28.2234   $28.22   $28.20   $28.20  
  Purchase #2 $127.27   3.612%   $131.867   $131.87   $131.85   $131.90  
  Purchase #3 $64.51   10.717%   $71.4235   $71.42   $71.40   $71.40  
  Purchase #4 $121.36   6.446%   $129.1829   $129.18   $129.20   $129.20  
  Purchase #5 $135.91   12.596%   $153.0292   $153.03   $153.05   $153.00  
  Purchase #6 $14.28   7.425%   $15.3403   $15.34   $15.35   $15.30  
  Purchase #7 $191.53   12.610%   $215.6819   $215.68   $215.70   $215.70  
  7 purchase totals = $679.66       $744.7482   $744.74   $744.75   $744.70