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	$243.36	13.126%	$275.3034	$275.30	$275.30	$275.30
Purchase #2	$26.89	6.662%	$28.6814	$28.68	$28.70	$28.70
Purchase #3	$227.80	13.573%	$258.7193	$258.72	$258.70	$258.70
Purchase #4	$121.55	4.801%	$127.3856	$127.39	$127.40	$127.40
Purchase #5	$248.85	11.233%	$276.8033	$276.80	$276.80	$276.80
Purchase #6	$165.82	5.246%	$174.5189	$174.52	$174.50	$174.50
Purchase #7	$176.80	6.846%	$188.9037	$188.90	$188.90	$188.90
7 purchase totals =	$1,211.07		$1,330.3156	$1,330.31	$1,330.30	$1,330.30