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	$35.96	8.636%	$39.0655	$39.07	$39.05	$39.10
Purchase #2	$116.27	10.211%	$128.1423	$128.14	$128.15	$128.10
Purchase #3	$226.75	6.660%	$241.8516	$241.85	$241.85	$241.90
Purchase #4	$241.46	3.671%	$250.324	$250.32	$250.30	$250.30
Purchase #5	$132.69	11.431%	$147.8578	$147.86	$147.85	$147.90
Purchase #6	$37.47	12.648%	$42.2092	$42.21	$42.20	$42.20
Purchase #7	$17.29	5.809%	$18.2944	$18.29	$18.30	$18.30
7 purchase totals =	$807.89		$867.7448	$867.74	$867.70	$867.80