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 $194.30   4.571%   $203.1815   $203.18   $203.20   $203.20  
  Purchase #2 $47.29   9.382%   $51.7267   $51.73   $51.75   $51.70  
  Purchase #3 $119.55   9.133%   $130.4685   $130.47   $130.45   $130.50  
  Purchase #4 $187.40   10.287%   $206.6778   $206.68   $206.70   $206.70  
  Purchase #5 $190.99   9.299%   $208.7502   $208.75   $208.75   $208.80  
  Purchase #6 $97.71   12.705%   $110.1241   $110.12   $110.10   $110.10  
  Purchase #7 $241.37   9.808%   $265.0436   $265.04   $265.05   $265.00  
  7 purchase totals = $1,078.61       $1,175.9724   $1,175.97   $1,176.00   $1,176.00