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 $59.53   13.677%   $67.6719   $67.67   $67.65   $67.70  
  Purchase #2 $136.43   11.800%   $152.5287   $152.53   $152.55   $152.50  
  Purchase #3 $114.82   3.735%   $119.1085   $119.11   $119.10   $119.10  
  Purchase #4 $46.79   9.384%   $51.1808   $51.18   $51.20   $51.20  
  Purchase #5 $201.45   8.672%   $218.9197   $218.92   $218.90   $218.90  
  Purchase #6 $93.43   5.142%   $98.2342   $98.23   $98.25   $98.20  
  Purchase #7 $164.48   5.262%   $173.1349   $173.13   $173.15   $173.10  
  7 purchase totals = $816.93       $880.7787   $880.77   $880.80   $880.70