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 $205.49   9.433%   $224.8739   $224.87   $224.85   $224.90  
  Purchase #2 $87.73   5.229%   $92.3174   $92.32   $92.30   $92.30  
  Purchase #3 $207.76   11.439%   $231.5257   $231.53   $231.55   $231.50  
  Purchase #4 $166.96   11.681%   $186.4626   $186.46   $186.45   $186.50  
  Purchase #5 $101.70   13.439%   $115.3675   $115.37   $115.35   $115.40  
  Purchase #6 $221.68   9.580%   $242.9169   $242.92   $242.90   $242.90  
  Purchase #7 $233.59   11.723%   $260.9738   $260.97   $260.95   $261.00  
  7 purchase totals = $1,224.91       $1,354.4378   $1,354.44   $1,354.35   $1,354.50