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 $59.87   3.181%   $61.7745   $61.77   $61.75   $61.80  
  Purchase #2 $114.66   9.208%   $125.2179   $125.22   $125.20   $125.20  
  Purchase #3 $10.50   13.725%   $11.9411   $11.94   $11.95   $11.90  
  Purchase #4 $225.34   13.800%   $256.4369   $256.44   $256.45   $256.40  
  Purchase #5 $180.73   11.278%   $201.1127   $201.11   $201.10   $201.10  
  Purchase #6 $48.63   6.549%   $51.8148   $51.81   $51.80   $51.80  
  Purchase #7 $208.75   9.259%   $228.0782   $228.08   $228.10   $228.10  
  7 purchase totals = $848.48       $936.3761   $936.37   $936.35   $936.30