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 $236.25   13.770%   $268.7816   $268.78   $268.80   $268.80  
  Purchase #2 $53.85   6.466%   $57.3319   $57.33   $57.35   $57.30  
  Purchase #3 $238.37   8.286%   $258.1213   $258.12   $258.10   $258.10  
  Purchase #4 $237.36   7.672%   $255.5703   $255.57   $255.55   $255.60  
  Purchase #5 $249.49   4.833%   $261.5479   $261.55   $261.55   $261.50  
  Purchase #6 $140.26   13.291%   $158.902   $158.90   $158.90   $158.90  
  Purchase #7 $165.75   12.504%   $186.4754   $186.48   $186.50   $186.50  
  7 purchase totals = $1,321.33       $1,446.7304   $1,446.73   $1,446.75   $1,446.70