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 $12.67   13.745%   $14.4115   $14.41   $14.40   $14.40  
  Purchase #2 $201.65   12.395%   $226.6445   $226.64   $226.65   $226.60  
  Purchase #3 $215.76   3.448%   $223.1994   $223.20   $223.20   $223.20  
  Purchase #4 $176.35   6.673%   $188.1178   $188.12   $188.10   $188.10  
  Purchase #5 $76.73   10.305%   $84.637   $84.64   $84.65   $84.60  
  Purchase #6 $120.50   8.292%   $130.4919   $130.49   $130.50   $130.50  
  Purchase #7 $231.29   10.312%   $255.1406   $255.14   $255.15   $255.10  
  7 purchase totals = $1,034.95       $1,122.6427   $1,122.64   $1,122.65   $1,122.50