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	$157.83	5.109%	$165.8935	$165.89	$165.90	$165.90
Purchase #2	$38.64	5.550%	$40.7845	$40.78	$40.80	$40.80
Purchase #3	$29.41	10.805%	$32.5878	$32.59	$32.60	$32.60
Purchase #4	$220.87	5.391%	$232.7771	$232.78	$232.80	$232.80
Purchase #5	$86.84	3.265%	$89.6753	$89.68	$89.70	$89.70
Purchase #6	$134.77	13.294%	$152.6863	$152.69	$152.70	$152.70
Purchase #7	$57.82	13.525%	$65.6402	$65.64	$65.65	$65.60
7 purchase totals =	$726.18		$780.0447	$780.05	$780.15	$780.10