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 $231.74   12.463%   $260.6218   $260.62   $260.60   $260.60  
  Purchase #2 $243.38   13.460%   $276.1389   $276.14   $276.15   $276.10  
  Purchase #3 $54.50   9.531%   $59.6944   $59.69   $59.70   $59.70  
  Purchase #4 $62.33   12.680%   $70.2334   $70.23   $70.25   $70.20  
  Purchase #5 $39.45   7.756%   $42.5097   $42.51   $42.50   $42.50  
  Purchase #6 $191.70   6.109%   $203.411   $203.41   $203.40   $203.40  
  Purchase #7 $117.91   6.835%   $125.9691   $125.97   $125.95   $126.00  
  7 purchase totals = $941.01       $1,038.5783   $1,038.57   $1,038.55   $1,038.50