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	$52.69	9.827%	$57.8678	$57.87	$57.85	$57.90
Purchase #2	$192.48	6.257%	$204.5235	$204.52	$204.50	$204.50
Purchase #3	$86.39	4.151%	$89.976	$89.98	$90.00	$90.00
Purchase #4	$182.84	9.123%	$199.5205	$199.52	$199.50	$199.50
Purchase #5	$158.28	9.344%	$173.0697	$173.07	$173.05	$173.10
Purchase #6	$85.45	7.249%	$91.6443	$91.64	$91.65	$91.60
Purchase #7	$249.58	12.600%	$281.0271	$281.03	$281.05	$281.00
7 purchase totals =	$1,007.71		$1,097.6289	$1,097.63	$1,097.60	$1,097.60