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	$138.71	7.321%	$148.865	$148.87	$148.85	$148.90
Purchase #2	$81.56	8.594%	$88.5693	$88.57	$88.55	$88.60
Purchase #3	$148.69	13.614%	$168.9327	$168.93	$168.95	$168.90
Purchase #4	$137.52	6.509%	$146.4712	$146.47	$146.45	$146.50
Purchase #5	$16.78	8.203%	$18.1565	$18.16	$18.15	$18.20
Purchase #6	$20.42	12.510%	$22.9745	$22.97	$22.95	$23.00
Purchase #7	$17.72	13.708%	$20.1491	$20.15	$20.15	$20.10
7 purchase totals =	$561.40		$614.1183	$614.12	$614.05	$614.20