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 $119.95   4.452%   $125.2902   $125.29   $125.30   $125.30  
  Purchase #2 $55.35   9.824%   $60.7876   $60.79   $60.80   $60.80  
  Purchase #3 $52.30   9.839%   $57.4458   $57.45   $57.45   $57.40  
  Purchase #4 $99.70   11.842%   $111.5065   $111.51   $111.50   $111.50  
  Purchase #5 $68.35   10.792%   $75.7263   $75.73   $75.75   $75.70  
  Purchase #6 $117.45   7.475%   $126.2294   $126.23   $126.25   $126.20  
  Purchase #7 $48.39   7.676%   $52.1044   $52.10   $52.10   $52.10  
  7 purchase totals = $561.49       $609.0902   $609.10   $609.15   $609.00