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	$237.37	13.448%	$269.2915	$269.29	$269.30	$269.30
Purchase #2	$16.54	8.160%	$17.8897	$17.89	$17.90	$17.90
Purchase #3	$105.56	10.741%	$116.8982	$116.90	$116.90	$116.90
Purchase #4	$81.42	5.533%	$85.925	$85.93	$85.95	$85.90
Purchase #5	$34.49	10.651%	$38.1635	$38.16	$38.15	$38.20
Purchase #6	$190.79	11.280%	$212.3111	$212.31	$212.30	$212.30
Purchase #7	$191.60	10.303%	$211.3405	$211.34	$211.35	$211.30
7 purchase totals =	$857.77		$951.8195	$951.82	$951.85	$951.80