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	$15.87	9.117%	$17.3169	$17.32	$17.30	$17.30
Purchase #2	$25.45	13.757%	$28.9512	$28.95	$28.95	$29.00
Purchase #3	$35.58	5.793%	$37.6411	$37.64	$37.65	$37.60
Purchase #4	$164.60	12.135%	$184.5742	$184.57	$184.55	$184.60
Purchase #5	$110.83	6.754%	$118.3155	$118.32	$118.30	$118.30
Purchase #6	$106.92	4.658%	$111.9003	$111.90	$111.90	$111.90
Purchase #7	$128.64	11.658%	$143.6369	$143.64	$143.65	$143.60
7 purchase totals =	$587.89		$642.3361	$642.34	$642.30	$642.30