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 $67.79   5.665%   $71.6303   $71.63   $71.65   $71.60  
  Purchase #2 $168.90   4.567%   $176.6137   $176.61   $176.60   $176.60  
  Purchase #3 $237.73   5.444%   $250.672   $250.67   $250.65   $250.70  
  Purchase #4 $54.46   10.851%   $60.3695   $60.37   $60.35   $60.40  
  Purchase #5 $148.42   8.569%   $161.1381   $161.14   $161.15   $161.10  
  Purchase #6 $48.63   3.212%   $50.192   $50.19   $50.20   $50.20  
  Purchase #7 $153.73   5.290%   $161.8623   $161.86   $161.85   $161.90  
  7 purchase totals = $879.66       $932.4779   $932.47   $932.45   $932.50