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	$37.81	9.407%	$41.3668	$41.37	$41.35	$41.40
Purchase #2	$116.68	13.456%	$132.3805	$132.38	$132.40	$132.40
Purchase #3	$174.35	12.515%	$196.1699	$196.17	$196.15	$196.20
Purchase #4	$223.61	10.533%	$247.1628	$247.16	$247.15	$247.20
Purchase #5	$11.61	13.801%	$13.2123	$13.21	$13.20	$13.20
Purchase #6	$10.92	11.340%	$12.1583	$12.16	$12.15	$12.20
Purchase #7	$10.74	8.283%	$11.6296	$11.63	$11.65	$11.60
7 purchase totals =	$585.72		$654.0802	$654.08	$654.05	$654.20