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 $241.94   12.863%   $273.0607   $273.06   $273.05   $273.10  
  Purchase #2 $67.89   10.510%   $75.0252   $75.03   $75.05   $75.00  
  Purchase #3 $46.77   7.284%   $50.1767   $50.18   $50.20   $50.20  
  Purchase #4 $15.86   9.331%   $17.3399   $17.34   $17.35   $17.30  
  Purchase #5 $234.87   11.336%   $261.4949   $261.49   $261.50   $261.50  
  Purchase #6 $117.67   5.563%   $124.216   $124.22   $124.20   $124.20  
  Purchase #7 $248.56   5.800%   $262.9765   $262.98   $263.00   $263.00  
  7 purchase totals = $973.56       $1,064.2899   $1,064.30   $1,064.35   $1,064.30