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 $101.51   3.134%   $104.6913   $104.69   $104.70   $104.70  
  Purchase #2 $175.92   11.115%   $195.4735   $195.47   $195.45   $195.50  
  Purchase #3 $43.93   5.341%   $46.2763   $46.28   $46.30   $46.30  
  Purchase #4 $115.31   11.309%   $128.3504   $128.35   $128.35   $128.40  
  Purchase #5 $192.60   12.370%   $216.4246   $216.42   $216.40   $216.40  
  Purchase #6 $234.72   11.223%   $261.0626   $261.06   $261.05   $261.10  
  Purchase #7 $205.47   6.182%   $218.1722   $218.17   $218.15   $218.20  
  7 purchase totals = $1,069.46       $1,170.4509   $1,170.44   $1,170.40   $1,170.60