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	$235.67	3.679%	$244.3403	$244.34	$244.35	$244.30
Purchase #2	$107.47	8.455%	$116.5566	$116.56	$116.55	$116.60
Purchase #3	$48.54	7.732%	$52.2931	$52.29	$52.30	$52.30
Purchase #4	$21.68	12.470%	$24.3835	$24.38	$24.40	$24.40
Purchase #5	$179.45	6.603%	$191.2991	$191.30	$191.30	$191.30
Purchase #6	$113.39	12.548%	$127.6182	$127.62	$127.60	$127.60
Purchase #7	$64.62	12.643%	$72.7899	$72.79	$72.80	$72.80
7 purchase totals =	$770.82		$829.2807	$829.28	$829.30	$829.30