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	$62.75	5.781%	$66.3776	$66.38	$66.40	$66.40
Purchase #2	$192.63	11.131%	$214.0716	$214.07	$214.05	$214.10
Purchase #3	$69.86	3.297%	$72.1633	$72.16	$72.15	$72.20
Purchase #4	$70.84	7.623%	$76.2401	$76.24	$76.25	$76.20
Purchase #5	$47.41	6.622%	$50.5495	$50.55	$50.55	$50.50
Purchase #6	$129.52	12.157%	$145.2657	$145.27	$145.25	$145.30
Purchase #7	$153.89	13.534%	$174.7175	$174.72	$174.70	$174.70
7 purchase totals =	$726.90		$799.3853	$799.39	$799.35	$799.40