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	$35.27	12.275%	$39.5994	$39.60	$39.60	$39.60
Purchase #2	$241.74	3.741%	$250.7835	$250.78	$250.80	$250.80
Purchase #3	$44.29	13.426%	$50.2364	$50.24	$50.25	$50.20
Purchase #4	$246.87	11.635%	$275.5933	$275.59	$275.60	$275.60
Purchase #5	$156.46	10.182%	$172.3908	$172.39	$172.40	$172.40
Purchase #6	$122.60	4.452%	$128.0582	$128.06	$128.05	$128.10
Purchase #7	$178.35	8.716%	$193.895	$193.90	$193.90	$193.90
7 purchase totals =	$1,025.58		$1,110.5566	$1,110.56	$1,110.60	$1,110.60