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	$39.53	8.603%	$42.9308	$42.93	$42.95	$42.90
Purchase #2	$91.58	6.461%	$97.497	$97.50	$97.50	$97.50
Purchase #3	$123.33	7.754%	$132.893	$132.89	$132.90	$132.90
Purchase #4	$39.91	5.178%	$41.9765	$41.98	$42.00	$42.00
Purchase #5	$151.52	9.221%	$165.4917	$165.49	$165.50	$165.50
Purchase #6	$143.56	12.188%	$161.0571	$161.06	$161.05	$161.10
Purchase #7	$153.64	4.129%	$159.9838	$159.98	$160.00	$160.00
7 purchase totals =	$743.07		$801.8299	$801.83	$801.90	$801.90