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	$18.82	8.427%	$20.406	$20.41	$20.40	$20.40
Purchase #2	$130.89	10.454%	$144.5732	$144.57	$144.55	$144.60
Purchase #3	$141.33	13.414%	$160.288	$160.29	$160.30	$160.30
Purchase #4	$132.86	7.826%	$143.2576	$143.26	$143.25	$143.30
Purchase #5	$111.60	8.135%	$120.6787	$120.68	$120.70	$120.70
Purchase #6	$218.83	6.748%	$233.5966	$233.60	$233.60	$233.60
Purchase #7	$216.85	13.307%	$245.7062	$245.71	$245.70	$245.70
7 purchase totals =	$971.18		$1,068.5063	$1,068.52	$1,068.50	$1,068.60