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	$138.29	13.867%	$157.4667	$157.47	$157.45	$157.50
Purchase #2	$51.52	11.298%	$57.3407	$57.34	$57.35	$57.30
Purchase #3	$186.64	10.730%	$206.6665	$206.67	$206.65	$206.70
Purchase #4	$185.34	6.582%	$197.5391	$197.54	$197.55	$197.50
Purchase #5	$63.83	13.227%	$72.2728	$72.27	$72.25	$72.30
Purchase #6	$107.80	3.117%	$111.1601	$111.16	$111.15	$111.20
Purchase #7	$172.45	11.308%	$191.9506	$191.95	$191.95	$192.00
7 purchase totals =	$905.87		$994.3965	$994.40	$994.35	$994.50