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	$172.32	10.530%	$190.4653	$190.47	$190.45	$190.50
Purchase #2	$183.77	3.321%	$189.873	$189.87	$189.85	$189.90
Purchase #3	$151.98	13.657%	$172.7359	$172.74	$172.75	$172.70
Purchase #4	$71.54	4.594%	$74.8265	$74.83	$74.85	$74.80
Purchase #5	$216.89	10.723%	$240.1471	$240.15	$240.15	$240.10
Purchase #6	$145.35	4.247%	$151.523	$151.52	$151.50	$151.50
Purchase #7	$64.51	10.486%	$71.2745	$71.27	$71.25	$71.30
7 purchase totals =	$1,006.36		$1,090.8453	$1,090.85	$1,090.80	$1,090.80