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 $59.46   9.197%   $64.9285   $64.93   $64.95   $64.90  
  Purchase #2 $214.56   6.697%   $228.9291   $228.93   $228.95   $228.90  
  Purchase #3 $117.47   11.307%   $130.7523   $130.75   $130.75   $130.80  
  Purchase #4 $12.49   10.265%   $13.7721   $13.77   $13.75   $13.80  
  Purchase #5 $98.58   9.549%   $107.9934   $107.99   $108.00   $108.00  
  Purchase #6 $64.44   11.553%   $71.8848   $71.88   $71.90   $71.90  
  Purchase #7 $204.68   4.243%   $213.3646   $213.36   $213.35   $213.40  
  7 purchase totals = $771.68       $831.6248   $831.61   $831.65   $831.70