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	$90.76	13.594%	$103.0979	$103.10	$103.10	$103.10
Purchase #2	$44.88	11.804%	$50.1776	$50.18	$50.20	$50.20
Purchase #3	$129.27	10.685%	$143.0825	$143.08	$143.10	$143.10
Purchase #4	$85.39	11.261%	$95.0058	$95.01	$95.00	$95.00
Purchase #5	$155.95	7.568%	$167.7523	$167.75	$167.75	$167.80
Purchase #6	$18.28	6.128%	$19.4002	$19.40	$19.40	$19.40
Purchase #7	$157.87	3.202%	$162.925	$162.93	$162.95	$162.90
7 purchase totals =	$682.40		$741.4413	$741.45	$741.50	$741.50