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	$73.53	13.593%	$83.5249	$83.52	$83.50	$83.50
Purchase #2	$209.66	11.429%	$233.622	$233.62	$233.60	$233.60
Purchase #3	$15.62	13.714%	$17.7621	$17.76	$17.75	$17.80
Purchase #4	$100.60	10.690%	$111.3541	$111.35	$111.35	$111.40
Purchase #5	$67.96	13.457%	$77.1054	$77.11	$77.10	$77.10
Purchase #6	$47.66	5.579%	$50.319	$50.32	$50.30	$50.30
Purchase #7	$30.50	11.626%	$34.0459	$34.05	$34.05	$34.00
7 purchase totals =	$545.53		$607.7334	$607.73	$607.65	$607.70