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	$249.56	5.847%	$264.1518	$264.15	$264.15	$264.20
Purchase #2	$56.92	4.859%	$59.6857	$59.69	$59.70	$59.70
Purchase #3	$39.40	13.115%	$44.5673	$44.57	$44.55	$44.60
Purchase #4	$242.52	8.680%	$263.5707	$263.57	$263.55	$263.60
Purchase #5	$118.81	6.263%	$126.2511	$126.25	$126.25	$126.30
Purchase #6	$152.61	8.346%	$165.3468	$165.35	$165.35	$165.30
Purchase #7	$50.58	10.391%	$55.8358	$55.84	$55.85	$55.80
7 purchase totals =	$910.40		$979.4092	$979.42	$979.40	$979.50