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	$9.61	12.714%	$10.8318	$10.83	$10.85	$10.80
Purchase #2	$225.35	13.662%	$256.1373	$256.14	$256.15	$256.10
Purchase #3	$192.78	13.213%	$218.252	$218.25	$218.25	$218.30
Purchase #4	$144.96	13.760%	$164.9065	$164.91	$164.90	$164.90
Purchase #5	$206.59	9.532%	$226.2822	$226.28	$226.30	$226.30
Purchase #6	$250.47	8.858%	$272.6566	$272.66	$272.65	$272.70
Purchase #7	$138.55	9.628%	$151.8896	$151.89	$151.90	$151.90
7 purchase totals =	$1,168.31		$1,300.9560	$1,300.96	$1,301.00	$1,301.00