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 $217.51   11.213%   $241.8994   $241.90   $241.90   $241.90  
  Purchase #2 $114.42   11.460%   $127.5325   $127.53   $127.55   $127.50  
  Purchase #3 $146.95   12.153%   $164.8088   $164.81   $164.80   $164.80  
  Purchase #4 $19.71   8.831%   $21.4506   $21.45   $21.45   $21.50  
  Purchase #5 $115.31   8.210%   $124.777   $124.78   $124.80   $124.80  
  Purchase #6 $218.82   5.194%   $230.1855   $230.19   $230.20   $230.20  
  Purchase #7 $26.40   8.318%   $28.596   $28.60   $28.60   $28.60  
  7 purchase totals = $859.12       $939.2498   $939.26   $939.30   $939.30