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 $249.30   13.493%   $282.938   $282.94   $282.95   $282.90  
  Purchase #2 $55.63   4.560%   $58.1667   $58.17   $58.15   $58.20  
  Purchase #3 $168.71   6.763%   $180.1199   $180.12   $180.10   $180.10  
  Purchase #4 $108.57   8.661%   $117.9732   $117.97   $117.95   $118.00  
  Purchase #5 $220.76   7.490%   $237.2949   $237.29   $237.30   $237.30  
  Purchase #6 $241.90   8.468%   $262.3841   $262.38   $262.40   $262.40  
  Purchase #7 $76.32   3.227%   $78.7828   $78.78   $78.80   $78.80  
  7 purchase totals = $1,121.19       $1,217.6596   $1,217.65   $1,217.65   $1,217.70