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 $57.66   9.175%   $62.9503   $62.95   $62.95   $63.00  
  Purchase #2 $204.48   6.343%   $217.4502   $217.45   $217.45   $217.50  
  Purchase #3 $173.73   8.714%   $188.8688   $188.87   $188.85   $188.90  
  Purchase #4 $46.59   4.841%   $48.8454   $48.85   $48.85   $48.80  
  Purchase #5 $54.98   11.435%   $61.267   $61.27   $61.25   $61.30  
  Purchase #6 $46.43   10.575%   $51.34   $51.34   $51.35   $51.30  
  Purchase #7 $18.54   3.468%   $19.183   $19.18   $19.20   $19.20  
  7 purchase totals = $602.41       $649.9047   $649.91   $649.90   $650.00