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 $243.75   10.253%   $268.7417   $268.74   $268.75   $268.70  
  Purchase #2 $79.39   8.834%   $86.4033   $86.40   $86.40   $86.40  
  Purchase #3 $217.85   3.232%   $224.8909   $224.89   $224.90   $224.90  
  Purchase #4 $229.34   12.291%   $257.5282   $257.53   $257.55   $257.50  
  Purchase #5 $109.79   3.242%   $113.3494   $113.35   $113.35   $113.30  
  Purchase #6 $209.61   5.672%   $221.4991   $221.50   $221.50   $221.50  
  Purchase #7 $114.74   12.335%   $128.8932   $128.89   $128.90   $128.90  
  7 purchase totals = $1,204.47       $1,301.3058   $1,301.30   $1,301.35   $1,301.20