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	$34.45	4.116%	$35.868	$35.87	$35.85	$35.90
Purchase #2	$127.83	10.394%	$141.1167	$141.12	$141.10	$141.10
Purchase #3	$42.55	6.572%	$45.3464	$45.35	$45.35	$45.30
Purchase #4	$50.66	9.586%	$55.5163	$55.52	$55.50	$55.50
Purchase #5	$219.34	8.636%	$238.2822	$238.28	$238.30	$238.30
Purchase #6	$79.54	10.138%	$87.6038	$87.60	$87.60	$87.60
Purchase #7	$207.52	13.674%	$235.8963	$235.90	$235.90	$235.90
7 purchase totals =	$761.89		$839.6297	$839.64	$839.60	$839.60