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 $73.57   3.652%   $76.2568   $76.26   $76.25   $76.30  
  Purchase #2 $47.75   7.790%   $51.4697   $51.47   $51.45   $51.50  
  Purchase #3 $105.36   12.112%   $118.1212   $118.12   $118.10   $118.10  
  Purchase #4 $100.94   6.533%   $107.5344   $107.53   $107.55   $107.50  
  Purchase #5 $117.93   9.792%   $129.4777   $129.48   $129.50   $129.50  
  Purchase #6 $114.73   9.247%   $125.3391   $125.34   $125.35   $125.30  
  Purchase #7 $164.33   13.352%   $186.2713   $186.27   $186.25   $186.30  
  7 purchase totals = $724.61       $794.4702   $794.47   $794.45   $794.50