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 $186.56   12.773%   $210.3893   $210.39   $210.40   $210.40  
  Purchase #2 $14.34   8.357%   $15.5384   $15.54   $15.55   $15.50  
  Purchase #3 $244.26   8.872%   $265.9307   $265.93   $265.95   $265.90  
  Purchase #4 $182.73   5.524%   $192.824   $192.82   $192.80   $192.80  
  Purchase #5 $75.36   4.176%   $78.507   $78.51   $78.50   $78.50  
  Purchase #6 $208.27   5.393%   $219.502   $219.50   $219.50   $219.50  
  Purchase #7 $237.60   10.157%   $261.733   $261.73   $261.75   $261.70  
  7 purchase totals = $1,149.12       $1,244.4244   $1,244.42   $1,244.45   $1,244.30