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	$83.38	8.371%	$90.3597	$90.36	$90.35	$90.40
Purchase #2	$151.90	4.489%	$158.7188	$158.72	$158.70	$158.70
Purchase #3	$8.36	3.300%	$8.6359	$8.64	$8.65	$8.60
Purchase #4	$9.41	12.388%	$10.5757	$10.58	$10.60	$10.60
Purchase #5	$140.32	7.212%	$150.4399	$150.44	$150.45	$150.40
Purchase #6	$31.49	5.435%	$33.2015	$33.20	$33.20	$33.20
Purchase #7	$101.77	3.625%	$105.4592	$105.46	$105.45	$105.50
7 purchase totals =	$526.63		$557.3907	$557.40	$557.40	$557.40