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	$163.84	5.338%	$172.5858	$172.59	$172.60	$172.60
Purchase #2	$207.77	10.482%	$229.5485	$229.55	$229.55	$229.50
Purchase #3	$92.79	11.698%	$103.6446	$103.64	$103.65	$103.60
Purchase #4	$231.87	5.330%	$244.2287	$244.23	$244.25	$244.20
Purchase #5	$155.98	6.858%	$166.6771	$166.68	$166.70	$166.70
Purchase #6	$224.45	4.865%	$235.3695	$235.37	$235.35	$235.40
Purchase #7	$34.34	9.504%	$37.6037	$37.60	$37.60	$37.60
7 purchase totals =	$1,111.04		$1,189.6579	$1,189.66	$1,189.70	$1,189.60