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	$160.27	11.292%	$178.3677	$178.37	$178.35	$178.40
Purchase #2	$141.48	5.784%	$149.6632	$149.66	$149.65	$149.70
Purchase #3	$39.60	5.225%	$41.6691	$41.67	$41.65	$41.70
Purchase #4	$141.49	6.775%	$151.0759	$151.08	$151.10	$151.10
Purchase #5	$11.95	11.480%	$13.3219	$13.32	$13.30	$13.30
Purchase #6	$165.83	4.342%	$173.0303	$173.03	$173.05	$173.00
Purchase #7	$81.25	9.847%	$89.2507	$89.25	$89.25	$89.30
7 purchase totals =	$741.87		$796.3788	$796.38	$796.35	$796.50