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 $55.56   12.723%   $62.6289   $62.63   $62.65   $62.60  
  Purchase #2 $230.73   3.567%   $238.9601   $238.96   $238.95   $239.00  
  Purchase #3 $78.81   8.403%   $85.4324   $85.43   $85.45   $85.40  
  Purchase #4 $219.38   4.476%   $229.1994   $229.20   $229.20   $229.20  
  Purchase #5 $8.27   12.324%   $9.2892   $9.29   $9.30   $9.30  
  Purchase #6 $127.43   12.296%   $143.0988   $143.10   $143.10   $143.10  
  Purchase #7 $57.89   7.687%   $62.34   $62.34   $62.35   $62.30  
  7 purchase totals = $778.07       $830.9488   $830.95   $831.00   $830.90