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 $202.25   5.487%   $213.3475   $213.35   $213.35   $213.30  
  Purchase #2 $152.42   10.128%   $167.8571   $167.86   $167.85   $167.90  
  Purchase #3 $231.66   12.291%   $260.1333   $260.13   $260.15   $260.10  
  Purchase #4 $235.85   3.832%   $244.8878   $244.89   $244.90   $244.90  
  Purchase #5 $235.44   11.874%   $263.3961   $263.40   $263.40   $263.40  
  Purchase #6 $207.68   5.199%   $218.4773   $218.48   $218.50   $218.50  
  Purchase #7 $54.86   6.188%   $58.2547   $58.25   $58.25   $58.30  
  7 purchase totals = $1,320.16       $1,426.3538   $1,426.36   $1,426.40   $1,426.40