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	$147.50	13.216%	$166.9936	$166.99	$167.00	$167.00
Purchase #2	$30.53	7.379%	$32.7828	$32.78	$32.80	$32.80
Purchase #3	$144.27	6.461%	$153.5913	$153.59	$153.60	$153.60
Purchase #4	$208.25	3.690%	$215.9344	$215.93	$215.95	$215.90
Purchase #5	$107.97	7.467%	$116.0321	$116.03	$116.05	$116.00
Purchase #6	$146.39	13.725%	$166.482	$166.48	$166.50	$166.50
Purchase #7	$35.48	5.806%	$37.54	$37.54	$37.55	$37.50
7 purchase totals =	$820.39		$889.3562	$889.34	$889.45	$889.30