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	$18.48	10.455%	$20.4121	$20.41	$20.40	$20.40
Purchase #2	$30.91	4.470%	$32.2917	$32.29	$32.30	$32.30
Purchase #3	$155.84	6.626%	$166.166	$166.17	$166.15	$166.20
Purchase #4	$138.87	6.629%	$148.0757	$148.08	$148.10	$148.10
Purchase #5	$116.52	12.771%	$131.4008	$131.40	$131.40	$131.40
Purchase #6	$124.25	8.379%	$134.6609	$134.66	$134.65	$134.70
Purchase #7	$40.25	13.276%	$45.5936	$45.59	$45.60	$45.60
7 purchase totals =	$625.12		$678.6008	$678.60	$678.60	$678.70