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	$104.74	6.244%	$111.28	$111.28	$111.30	$111.30
Purchase #2	$108.54	13.862%	$123.5858	$123.59	$123.60	$123.60
Purchase #3	$106.31	13.747%	$120.9244	$120.92	$120.90	$120.90
Purchase #4	$21.63	7.816%	$23.3206	$23.32	$23.30	$23.30
Purchase #5	$136.93	9.178%	$149.4974	$149.50	$149.50	$149.50
Purchase #6	$81.99	11.683%	$91.5689	$91.57	$91.55	$91.60
Purchase #7	$107.93	7.847%	$116.3993	$116.40	$116.40	$116.40
7 purchase totals =	$668.07		$736.5764	$736.58	$736.55	$736.60