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	$85.41	5.454%	$90.0683	$90.07	$90.05	$90.10
Purchase #2	$77.26	10.613%	$85.4596	$85.46	$85.45	$85.50
Purchase #3	$51.83	8.800%	$56.391	$56.39	$56.40	$56.40
Purchase #4	$203.62	10.707%	$225.4216	$225.42	$225.40	$225.40
Purchase #5	$143.41	8.491%	$155.5869	$155.59	$155.60	$155.60
Purchase #6	$35.95	3.711%	$37.2841	$37.28	$37.30	$37.30
Purchase #7	$28.28	9.504%	$30.9677	$30.97	$30.95	$31.00
7 purchase totals =	$625.76		$681.1792	$681.18	$681.15	$681.30