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	$211.87	6.181%	$224.9657	$224.97	$224.95	$225.00
Purchase #2	$120.63	5.655%	$127.4516	$127.45	$127.45	$127.50
Purchase #3	$124.68	7.701%	$134.2816	$134.28	$134.30	$134.30
Purchase #4	$139.41	13.679%	$158.4799	$158.48	$158.50	$158.50
Purchase #5	$52.39	10.247%	$57.7584	$57.76	$57.75	$57.80
Purchase #6	$90.68	10.632%	$100.3211	$100.32	$100.30	$100.30
Purchase #7	$94.84	9.751%	$104.0878	$104.09	$104.10	$104.10
7 purchase totals =	$834.50		$907.3461	$907.35	$907.35	$907.50