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	$82.82	9.483%	$90.6738	$90.67	$90.65	$90.70
Purchase #2	$126.83	4.232%	$132.1974	$132.20	$132.20	$132.20
Purchase #3	$115.88	9.607%	$127.0126	$127.01	$127.00	$127.00
Purchase #4	$9.34	10.456%	$10.3166	$10.32	$10.30	$10.30
Purchase #5	$167.35	13.281%	$189.5758	$189.58	$189.60	$189.60
Purchase #6	$33.52	5.517%	$35.3693	$35.37	$35.35	$35.40
Purchase #7	$222.79	5.552%	$235.1593	$235.16	$235.15	$235.20
7 purchase totals =	$758.53		$820.3048	$820.31	$820.25	$820.40