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	$114.31	13.359%	$129.5807	$129.58	$129.60	$129.60
Purchase #2	$26.74	5.593%	$28.2356	$28.24	$28.25	$28.20
Purchase #3	$208.81	12.570%	$235.0574	$235.06	$235.05	$235.10
Purchase #4	$207.59	13.368%	$235.3406	$235.34	$235.35	$235.30
Purchase #5	$105.84	5.300%	$111.4495	$111.45	$111.45	$111.40
Purchase #6	$181.42	8.326%	$196.525	$196.53	$196.55	$196.50
Purchase #7	$52.77	12.757%	$59.5019	$59.50	$59.50	$59.50
7 purchase totals =	$897.48		$995.6907	$995.70	$995.75	$995.60