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	$212.83	12.717%	$239.8956	$239.90	$239.90	$239.90
Purchase #2	$117.65	12.435%	$132.2798	$132.28	$132.30	$132.30
Purchase #3	$140.60	3.842%	$146.0019	$146.00	$146.00	$146.00
Purchase #4	$83.40	8.520%	$90.5057	$90.51	$90.50	$90.50
Purchase #5	$92.35	10.849%	$102.3691	$102.37	$102.35	$102.40
Purchase #6	$13.42	5.114%	$14.1063	$14.11	$14.10	$14.10
Purchase #7	$179.56	3.322%	$185.525	$185.53	$185.55	$185.50
7 purchase totals =	$839.81		$910.6834	$910.70	$910.70	$910.70