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 $248.39   5.196%   $261.2963   $261.30   $261.30   $261.30  
  Purchase #2 $154.62   8.627%   $167.9591   $167.96   $167.95   $168.00  
  Purchase #3 $243.89   4.719%   $255.3992   $255.40   $255.40   $255.40  
  Purchase #4 $80.61   8.249%   $87.2595   $87.26   $87.25   $87.30  
  Purchase #5 $174.37   12.431%   $196.0459   $196.05   $196.05   $196.00  
  Purchase #6 $200.76   8.676%   $218.1779   $218.18   $218.20   $218.20  
  Purchase #7 $83.90   13.827%   $95.5009   $95.50   $95.50   $95.50  
  7 purchase totals = $1,186.54       $1,281.6388   $1,281.65   $1,281.65   $1,281.70