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 $168.89   13.162%   $191.1193   $191.12   $191.10   $191.10  
  Purchase #2 $241.61   8.304%   $261.6733   $261.67   $261.65   $261.70  
  Purchase #3 $82.99   8.663%   $90.1794   $90.18   $90.20   $90.20  
  Purchase #4 $236.98   4.256%   $247.0659   $247.07   $247.05   $247.10  
  Purchase #5 $27.43   10.346%   $30.2679   $30.27   $30.25   $30.30  
  Purchase #6 $123.42   10.207%   $136.0175   $136.02   $136.00   $136.00  
  Purchase #7 $240.90   3.462%   $249.24   $249.24   $249.25   $249.20  
  7 purchase totals = $1,122.22       $1,205.5633   $1,205.57   $1,205.50   $1,205.60