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	$238.48	7.114%	$255.4455	$255.45	$255.45	$255.40
Purchase #2	$93.90	8.275%	$101.6702	$101.67	$101.65	$101.70
Purchase #3	$202.35	13.743%	$230.159	$230.16	$230.15	$230.20
Purchase #4	$14.52	5.282%	$15.2869	$15.29	$15.30	$15.30
Purchase #5	$50.33	9.492%	$55.1073	$55.11	$55.10	$55.10
Purchase #6	$51.41	6.491%	$54.747	$54.75	$54.75	$54.70
Purchase #7	$53.56	10.487%	$59.1768	$59.18	$59.20	$59.20
7 purchase totals =	$704.55		$771.5927	$771.61	$771.60	$771.60