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 $218.53   13.623%   $248.3003   $248.30   $248.30   $248.30  
  Purchase #2 $171.68   9.446%   $187.8969   $187.90   $187.90   $187.90  
  Purchase #3 $100.79   4.404%   $105.2288   $105.23   $105.25   $105.20  
  Purchase #4 $34.51   11.313%   $38.4141   $38.41   $38.40   $38.40  
  Purchase #5 $226.33   4.482%   $236.4741   $236.47   $236.45   $236.50  
  Purchase #6 $239.97   8.766%   $261.0058   $261.01   $261.00   $261.00  
  Purchase #7 $162.58   3.578%   $168.3971   $168.40   $168.40   $168.40  
  7 purchase totals = $1,154.39       $1,245.7171   $1,245.72   $1,245.70   $1,245.70