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	$235.94	6.174%	$250.5069	$250.51	$250.50	$250.50
Purchase #2	$94.89	11.129%	$105.4503	$105.45	$105.45	$105.50
Purchase #3	$152.67	4.123%	$158.9646	$158.96	$158.95	$159.00
Purchase #4	$162.75	11.767%	$181.9008	$181.90	$181.90	$181.90
Purchase #5	$214.55	10.129%	$236.2818	$236.28	$236.30	$236.30
Purchase #6	$172.58	12.665%	$194.4373	$194.44	$194.45	$194.40
Purchase #7	$146.99	3.716%	$152.4521	$152.45	$152.45	$152.50
7 purchase totals =	$1,180.37		$1,279.9938	$1,279.99	$1,280.00	$1,280.10