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 $72.74   6.712%   $77.6223   $77.62   $77.60   $77.60  
  Purchase #2 $155.83   12.424%   $175.1903   $175.19   $175.20   $175.20  
  Purchase #3 $132.34   4.131%   $137.807   $137.81   $137.80   $137.80  
  Purchase #4 $214.80   11.868%   $240.2925   $240.29   $240.30   $240.30  
  Purchase #5 $216.63   9.619%   $237.4676   $237.47   $237.45   $237.50  
  Purchase #6 $158.81   7.643%   $170.9478   $170.95   $170.95   $170.90  
  Purchase #7 $202.99   5.674%   $214.5077   $214.51   $214.50   $214.50  
  7 purchase totals = $1,154.14       $1,253.8352   $1,253.84   $1,253.80   $1,253.80