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	$247.29	3.789%	$256.6598	$256.66	$256.65	$256.70
Purchase #2	$42.42	13.537%	$48.1624	$48.16	$48.15	$48.20
Purchase #3	$91.76	8.444%	$99.5082	$99.51	$99.50	$99.50
Purchase #4	$157.38	6.299%	$167.2934	$167.29	$167.30	$167.30
Purchase #5	$13.76	13.801%	$15.659	$15.66	$15.65	$15.70
Purchase #6	$146.39	4.513%	$152.9966	$153.00	$153.00	$153.00
Purchase #7	$103.59	13.444%	$117.5166	$117.52	$117.50	$117.50
7 purchase totals =	$802.59		$857.7960	$857.80	$857.75	$857.90