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 $11.61   4.261%   $12.1047   $12.10   $12.10   $12.10  
  Purchase #2 $91.35   13.661%   $103.8293   $103.83   $103.85   $103.80  
  Purchase #3 $69.63   5.383%   $73.3782   $73.38   $73.40   $73.40  
  Purchase #4 $119.79   8.123%   $129.5205   $129.52   $129.50   $129.50  
  Purchase #5 $206.76   3.152%   $213.2771   $213.28   $213.30   $213.30  
  Purchase #6 $121.44   3.175%   $125.2957   $125.30   $125.30   $125.30  
  Purchase #7 $122.87   8.350%   $133.1296   $133.13   $133.15   $133.10  
  7 purchase totals = $743.45       $790.5351   $790.54   $790.60   $790.50