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 $41.34   13.530%   $46.9333   $46.93   $46.95   $46.90  
  Purchase #2 $135.42   4.319%   $141.2688   $141.27   $141.25   $141.30  
  Purchase #3 $50.76   13.809%   $57.7694   $57.77   $57.75   $57.80  
  Purchase #4 $178.49   8.299%   $193.3029   $193.30   $193.30   $193.30  
  Purchase #5 $151.99   7.868%   $163.9486   $163.95   $163.95   $163.90  
  Purchase #6 $202.82   10.521%   $224.1587   $224.16   $224.15   $224.20  
  Purchase #7 $62.43   5.132%   $65.6339   $65.63   $65.65   $65.60  
  7 purchase totals = $823.25       $893.0156   $893.01   $893.00   $893.00