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 $44.71   12.567%   $50.3287   $50.33   $50.35   $50.30  
  Purchase #2 $51.34   10.412%   $56.6855   $56.69   $56.70   $56.70  
  Purchase #3 $224.75   9.466%   $246.0248   $246.02   $246.00   $246.00  
  Purchase #4 $188.36   5.277%   $198.2998   $198.30   $198.30   $198.30  
  Purchase #5 $172.41   7.622%   $185.5511   $185.55   $185.55   $185.60  
  Purchase #6 $174.86   4.225%   $182.2478   $182.25   $182.25   $182.20  
  Purchase #7 $112.39   11.272%   $125.0586   $125.06   $125.05   $125.10  
  7 purchase totals = $968.82       $1,044.1963   $1,044.20   $1,044.20   $1,044.20