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	$32.72	7.479%	$35.1671	$35.17	$35.15	$35.20
Purchase #2	$173.27	4.121%	$180.4105	$180.41	$180.40	$180.40
Purchase #3	$19.77	10.195%	$21.7856	$21.79	$21.80	$21.80
Purchase #4	$225.65	3.327%	$233.1574	$233.16	$233.15	$233.20
Purchase #5	$97.79	7.473%	$105.0978	$105.10	$105.10	$105.10
Purchase #6	$32.86	4.801%	$34.4376	$34.44	$34.45	$34.40
Purchase #7	$58.45	3.222%	$60.3333	$60.33	$60.35	$60.30
7 purchase totals =	$640.51		$670.3893	$670.40	$670.40	$670.40