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	$90.27	13.643%	$102.5855	$102.59	$102.60	$102.60
Purchase #2	$128.78	13.849%	$146.6147	$146.61	$146.60	$146.60
Purchase #3	$247.32	9.831%	$271.634	$271.63	$271.65	$271.60
Purchase #4	$39.68	13.175%	$44.9078	$44.91	$44.90	$44.90
Purchase #5	$55.89	3.306%	$57.7377	$57.74	$57.75	$57.70
Purchase #6	$143.33	10.379%	$158.2062	$158.21	$158.20	$158.20
Purchase #7	$105.88	5.253%	$111.4419	$111.44	$111.45	$111.40
7 purchase totals =	$811.15		$893.1278	$893.13	$893.15	$893.00