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 $53.71   5.193%   $56.4992   $56.50   $56.50   $56.50  
  Purchase #2 $151.98   11.812%   $169.9319   $169.93   $169.95   $169.90  
  Purchase #3 $78.95   6.393%   $83.9973   $84.00   $84.00   $84.00  
  Purchase #4 $57.90   10.175%   $63.7913   $63.79   $63.80   $63.80  
  Purchase #5 $42.66   10.606%   $47.1845   $47.18   $47.20   $47.20  
  Purchase #6 $195.81   4.364%   $204.3551   $204.36   $204.35   $204.40  
  Purchase #7 $127.45   4.722%   $133.4682   $133.47   $133.45   $133.50  
  7 purchase totals = $708.46       $759.2275   $759.23   $759.25   $759.30