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 $118.25   6.712%   $126.1869   $126.19   $126.20   $126.20  
  Purchase #2 $110.62   13.796%   $125.8811   $125.88   $125.90   $125.90  
  Purchase #3 $55.54   6.850%   $59.3445   $59.34   $59.35   $59.30  
  Purchase #4 $14.48   11.588%   $16.1579   $16.16   $16.15   $16.20  
  Purchase #5 $48.64   4.299%   $50.731   $50.73   $50.75   $50.70  
  Purchase #6 $245.27   5.296%   $258.2595   $258.26   $258.25   $258.30  
  Purchase #7 $178.39   7.484%   $191.7407   $191.74   $191.75   $191.70  
  7 purchase totals = $771.19       $828.3016   $828.30   $828.35   $828.30