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	$162.26	6.727%	$173.1752	$173.18	$173.20	$173.20
Purchase #2	$128.66	12.288%	$144.4697	$144.47	$144.45	$144.50
Purchase #3	$150.37	10.135%	$165.61	$165.61	$165.60	$165.60
Purchase #4	$101.35	4.198%	$105.6047	$105.60	$105.60	$105.60
Purchase #5	$99.85	5.710%	$105.5514	$105.55	$105.55	$105.60
Purchase #6	$48.70	7.264%	$52.2376	$52.24	$52.25	$52.20
Purchase #7	$31.88	9.771%	$34.995	$35.00	$35.00	$35.00
7 purchase totals =	$723.07		$781.6436	$781.65	$781.65	$781.70