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 $213.96   5.867%   $226.513   $226.51   $226.50   $226.50  
  Purchase #2 $166.34   6.205%   $176.6614   $176.66   $176.65   $176.70  
  Purchase #3 $42.99   4.526%   $44.9357   $44.94   $44.95   $44.90  
  Purchase #4 $105.51   4.611%   $110.3751   $110.38   $110.40   $110.40  
  Purchase #5 $83.87   12.766%   $94.5768   $94.58   $94.60   $94.60  
  Purchase #6 $244.94   12.428%   $275.3811   $275.38   $275.40   $275.40  
  Purchase #7 $27.93   10.334%   $30.8163   $30.82   $30.80   $30.80  
  7 purchase totals = $885.54       $959.2594   $959.27   $959.30   $959.30