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 $214.89   13.796%   $244.5362   $244.54   $244.55   $244.50  
  Purchase #2 $120.86   10.433%   $133.4693   $133.47   $133.45   $133.50  
  Purchase #3 $189.39   13.278%   $214.5372   $214.54   $214.55   $214.50  
  Purchase #4 $250.97   6.170%   $266.4548   $266.45   $266.45   $266.50  
  Purchase #5 $222.86   12.133%   $249.8996   $249.90   $249.90   $249.90  
  Purchase #6 $28.36   13.869%   $32.2932   $32.29   $32.30   $32.30  
  Purchase #7 $125.34   9.119%   $136.7698   $136.77   $136.75   $136.80  
  7 purchase totals = $1,152.67       $1,277.9601   $1,277.96   $1,277.95   $1,278.00