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	$15.77	12.415%	$17.7278	$17.73	$17.75	$17.70
Purchase #2	$249.58	11.464%	$278.1919	$278.19	$278.20	$278.20
Purchase #3	$90.36	10.721%	$100.0475	$100.05	$100.05	$100.00
Purchase #4	$182.31	13.299%	$206.5554	$206.56	$206.55	$206.60
Purchase #5	$184.60	12.749%	$208.1347	$208.13	$208.15	$208.10
Purchase #6	$33.75	10.122%	$37.1662	$37.17	$37.15	$37.20
Purchase #7	$86.82	4.457%	$90.6896	$90.69	$90.70	$90.70
7 purchase totals =	$843.19		$938.5131	$938.52	$938.55	$938.50