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 $215.42   13.674%   $244.8765   $244.88   $244.90   $244.90  
  Purchase #2 $212.57   11.563%   $237.1495   $237.15   $237.15   $237.10  
  Purchase #3 $149.96   9.401%   $164.0577   $164.06   $164.05   $164.10  
  Purchase #4 $190.62   8.859%   $207.507   $207.51   $207.50   $207.50  
  Purchase #5 $124.72   10.375%   $137.6597   $137.66   $137.65   $137.70  
  Purchase #6 $101.97   5.328%   $107.403   $107.40   $107.40   $107.40  
  Purchase #7 $121.36   3.252%   $125.3066   $125.31   $125.30   $125.30  
  7 purchase totals = $1,116.62       $1,223.9600   $1,223.97   $1,223.95   $1,224.00