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	$27.61	7.258%	$29.6139	$29.61	$29.60	$29.60
Purchase #2	$35.95	4.517%	$37.5739	$37.57	$37.55	$37.60
Purchase #3	$12.91	12.447%	$14.5169	$14.52	$14.50	$14.50
Purchase #4	$109.84	6.377%	$116.8445	$116.84	$116.85	$116.80
Purchase #5	$107.65	9.766%	$118.1631	$118.16	$118.15	$118.20
Purchase #6	$231.83	7.443%	$249.0851	$249.09	$249.10	$249.10
Purchase #7	$164.39	10.793%	$182.1326	$182.13	$182.15	$182.10
7 purchase totals =	$690.18		$747.9300	$747.92	$747.90	$747.90