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 $221.89   13.186%   $251.1484   $251.15   $251.15   $251.10  
  Purchase #2 $230.39   13.102%   $260.5757   $260.58   $260.60   $260.60  
  Purchase #3 $117.69   6.433%   $125.261   $125.26   $125.25   $125.30  
  Purchase #4 $141.56   3.447%   $146.4396   $146.44   $146.45   $146.40  
  Purchase #5 $175.46   11.494%   $195.6274   $195.63   $195.65   $195.60  
  Purchase #6 $232.58   4.308%   $242.5995   $242.60   $242.60   $242.60  
  Purchase #7 $48.91   13.188%   $55.3603   $55.36   $55.35   $55.40  
  7 purchase totals = $1,168.48       $1,277.0119   $1,277.02   $1,277.05   $1,277.00