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	$108.58	13.795%	$123.5586	$123.56	$123.55	$123.60
Purchase #2	$244.40	4.678%	$255.833	$255.83	$255.85	$255.80
Purchase #3	$117.92	13.467%	$133.8003	$133.80	$133.80	$133.80
Purchase #4	$162.93	7.727%	$175.5196	$175.52	$175.50	$175.50
Purchase #5	$250.55	8.708%	$272.3679	$272.37	$272.35	$272.40
Purchase #6	$163.89	5.218%	$172.4418	$172.44	$172.45	$172.40
Purchase #7	$73.42	6.719%	$78.3531	$78.35	$78.35	$78.40
7 purchase totals =	$1,121.69		$1,211.8743	$1,211.87	$1,211.85	$1,211.90