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	$5.86	11.498%	$6.5338	$6.53	$6.55	$6.50
Purchase #2	$225.76	13.568%	$256.3911	$256.39	$256.40	$256.40
Purchase #3	$134.69	10.455%	$148.7718	$148.77	$148.75	$148.80
Purchase #4	$143.43	13.312%	$162.5234	$162.52	$162.50	$162.50
Purchase #5	$146.58	8.240%	$158.6582	$158.66	$158.65	$158.70
Purchase #6	$154.73	7.433%	$166.2311	$166.23	$166.25	$166.20
Purchase #7	$170.42	10.495%	$188.3056	$188.31	$188.30	$188.30
7 purchase totals =	$981.47		$1,087.4150	$1,087.41	$1,087.40	$1,087.40