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	$165.77	4.245%	$172.8069	$172.81	$172.80	$172.80
Purchase #2	$117.35	5.196%	$123.4475	$123.45	$123.45	$123.40
Purchase #3	$64.37	10.191%	$70.9299	$70.93	$70.95	$70.90
Purchase #4	$46.87	3.531%	$48.525	$48.53	$48.55	$48.50
Purchase #5	$96.73	8.626%	$105.0739	$105.07	$105.05	$105.10
Purchase #6	$169.60	12.817%	$191.3376	$191.34	$191.35	$191.30
Purchase #7	$84.50	7.299%	$90.6677	$90.67	$90.65	$90.70
7 purchase totals =	$745.19		$802.7885	$802.80	$802.80	$802.70