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	$104.85	13.658%	$119.1704	$119.17	$119.15	$119.20
Purchase #2	$34.55	11.299%	$38.4538	$38.45	$38.45	$38.50
Purchase #3	$71.47	8.139%	$77.2869	$77.29	$77.30	$77.30
Purchase #4	$71.98	13.316%	$81.5649	$81.56	$81.55	$81.60
Purchase #5	$86.88	10.140%	$95.6896	$95.69	$95.70	$95.70
Purchase #6	$17.40	5.543%	$18.3645	$18.36	$18.35	$18.40
Purchase #7	$226.27	6.429%	$240.8169	$240.82	$240.80	$240.80
7 purchase totals =	$613.40		$671.3470	$671.34	$671.30	$671.50