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	$95.71	10.116%	$105.392	$105.39	$105.40	$105.40
Purchase #2	$87.36	7.854%	$94.2213	$94.22	$94.20	$94.20
Purchase #3	$107.65	13.649%	$122.3431	$122.34	$122.35	$122.30
Purchase #4	$89.75	11.583%	$100.1457	$100.15	$100.15	$100.10
Purchase #5	$89.32	10.120%	$98.3592	$98.36	$98.35	$98.40
Purchase #6	$110.55	12.422%	$124.2825	$124.28	$124.30	$124.30
Purchase #7	$19.26	7.870%	$20.7758	$20.78	$20.80	$20.80
7 purchase totals =	$599.60		$665.5196	$665.52	$665.55	$665.50