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 $226.78   3.709%   $235.1913   $235.19   $235.20   $235.20  
  Purchase #2 $167.92   8.543%   $182.2654   $182.27   $182.25   $182.30  
  Purchase #3 $199.33   4.192%   $207.6859   $207.69   $207.70   $207.70  
  Purchase #4 $172.69   10.309%   $190.4926   $190.49   $190.50   $190.50  
  Purchase #5 $249.74   8.265%   $270.381   $270.38   $270.40   $270.40  
  Purchase #6 $110.87   6.402%   $117.9679   $117.97   $117.95   $118.00  
  Purchase #7 $175.36   7.742%   $188.9364   $188.94   $188.95   $188.90  
  7 purchase totals = $1,302.69       $1,392.9205   $1,392.93   $1,392.95   $1,393.00