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 $233.87   6.557%   $249.2049   $249.20   $249.20   $249.20  
  Purchase #2 $249.93   11.854%   $279.5567   $279.56   $279.55   $279.60  
  Purchase #3 $91.75   7.314%   $98.4606   $98.46   $98.45   $98.50  
  Purchase #4 $249.75   7.668%   $268.9008   $268.90   $268.90   $268.90  
  Purchase #5 $207.31   10.750%   $229.5958   $229.60   $229.60   $229.60  
  Purchase #6 $92.91   6.354%   $98.8135   $98.81   $98.80   $98.80  
  Purchase #7 $115.41   8.131%   $124.794   $124.79   $124.80   $124.80  
  7 purchase totals = $1,240.93       $1,349.3263   $1,349.32   $1,349.30   $1,349.40