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 $144.51   4.863%   $151.5375   $151.54   $151.55   $151.50  
  Purchase #2 $250.43   9.397%   $273.9629   $273.96   $273.95   $274.00  
  Purchase #3 $141.94   13.685%   $161.3645   $161.36   $161.35   $161.40  
  Purchase #4 $133.95   8.344%   $145.1268   $145.13   $145.15   $145.10  
  Purchase #5 $241.77   8.261%   $261.7426   $261.74   $261.75   $261.70  
  Purchase #6 $12.88   13.523%   $14.6218   $14.62   $14.60   $14.60  
  Purchase #7 $147.64   9.643%   $161.8769   $161.88   $161.90   $161.90  
  7 purchase totals = $1,073.12       $1,170.2330   $1,170.23   $1,170.25   $1,170.20