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	$54.85	10.103%	$60.3915	$60.39	$60.40	$60.40
Purchase #2	$180.76	5.393%	$190.5084	$190.51	$190.50	$190.50
Purchase #3	$82.39	11.153%	$91.579	$91.58	$91.60	$91.60
Purchase #4	$38.49	4.396%	$40.182	$40.18	$40.20	$40.20
Purchase #5	$83.55	7.724%	$90.0034	$90.00	$90.00	$90.00
Purchase #6	$137.32	13.787%	$156.2523	$156.25	$156.25	$156.30
Purchase #7	$65.87	3.853%	$68.408	$68.41	$68.40	$68.40
7 purchase totals =	$643.23		$697.3246	$697.32	$697.35	$697.40