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	$214.68	6.847%	$229.3791	$229.38	$229.40	$229.40
Purchase #2	$46.56	12.429%	$52.3469	$52.35	$52.35	$52.30
Purchase #3	$156.72	9.422%	$171.4862	$171.49	$171.50	$171.50
Purchase #4	$66.65	6.764%	$71.1582	$71.16	$71.15	$71.20
Purchase #5	$103.94	7.503%	$111.7386	$111.74	$111.75	$111.70
Purchase #6	$124.33	11.252%	$138.3196	$138.32	$138.30	$138.30
Purchase #7	$63.55	4.720%	$66.5496	$66.55	$66.55	$66.50
7 purchase totals =	$776.43		$840.9782	$840.99	$841.00	$840.90