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 $136.64   5.611%   $144.3069   $144.31   $144.30   $144.30  
  Purchase #2 $143.57   12.161%   $161.0295   $161.03   $161.05   $161.00  
  Purchase #3 $15.25   13.271%   $17.2738   $17.27   $17.25   $17.30  
  Purchase #4 $161.86   8.388%   $175.4368   $175.44   $175.45   $175.40  
  Purchase #5 $114.92   4.671%   $120.2879   $120.29   $120.30   $120.30  
  Purchase #6 $186.43   11.308%   $207.5115   $207.51   $207.50   $207.50  
  Purchase #7 $191.87   10.183%   $211.4081   $211.41   $211.40   $211.40  
  7 purchase totals = $950.54       $1,037.2545   $1,037.26   $1,037.25   $1,037.20