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 $208.58   13.510%   $236.7592   $236.76   $236.75   $236.80  
  Purchase #2 $39.29   13.539%   $44.6095   $44.61   $44.60   $44.60  
  Purchase #3 $198.84   3.532%   $205.863   $205.86   $205.85   $205.90  
  Purchase #4 $133.67   8.658%   $145.2431   $145.24   $145.25   $145.20  
  Purchase #5 $158.74   12.233%   $178.1587   $178.16   $178.15   $178.20  
  Purchase #6 $235.99   3.683%   $244.6815   $244.68   $244.70   $244.70  
  Purchase #7 $17.37   6.855%   $18.5607   $18.56   $18.55   $18.60  
  7 purchase totals = $992.48       $1,073.8757   $1,073.87   $1,073.85   $1,074.00