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 $25.65   3.818%   $26.6293   $26.63   $26.65   $26.60  
  Purchase #2 $159.47   11.275%   $177.4502   $177.45   $177.45   $177.50  
  Purchase #3 $86.94   5.359%   $91.5991   $91.60   $91.60   $91.60  
  Purchase #4 $118.33   11.211%   $131.596   $131.60   $131.60   $131.60  
  Purchase #5 $117.54   12.439%   $132.1608   $132.16   $132.15   $132.20  
  Purchase #6 $158.95   7.143%   $170.3038   $170.30   $170.30   $170.30  
  Purchase #7 $113.32   5.176%   $119.1854   $119.19   $119.20   $119.20  
  7 purchase totals = $780.20       $848.9246   $848.93   $848.95   $849.00