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 $170.90   6.483%   $181.9794   $181.98   $182.00   $182.00  
  Purchase #2 $213.72   6.553%   $227.7251   $227.73   $227.75   $227.70  
  Purchase #3 $116.99   13.852%   $133.1955   $133.20   $133.20   $133.20  
  Purchase #4 $243.58   7.262%   $261.2688   $261.27   $261.25   $261.30  
  Purchase #5 $211.48   11.832%   $236.5023   $236.50   $236.50   $236.50  
  Purchase #6 $108.98   5.391%   $114.8551   $114.86   $114.85   $114.90  
  Purchase #7 $44.25   9.430%   $48.4228   $48.42   $48.40   $48.40  
  7 purchase totals = $1,109.90       $1,203.9490   $1,203.96   $1,203.95   $1,204.00