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	$40.27	12.420%	$45.2715	$45.27	$45.25	$45.30
Purchase #2	$167.56	12.704%	$188.8468	$188.85	$188.85	$188.80
Purchase #3	$74.60	3.413%	$77.1461	$77.15	$77.15	$77.10
Purchase #4	$54.85	4.834%	$57.5014	$57.50	$57.50	$57.50
Purchase #5	$53.67	9.761%	$58.9087	$58.91	$58.90	$58.90
Purchase #6	$83.75	5.612%	$88.4501	$88.45	$88.45	$88.50
Purchase #7	$143.63	3.405%	$148.5206	$148.52	$148.50	$148.50
7 purchase totals =	$618.33		$664.6452	$664.65	$664.60	$664.60