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	$153.55	7.592%	$165.2075	$165.21	$165.20	$165.20
Purchase #2	$93.59	6.846%	$99.9972	$100.00	$100.00	$100.00
Purchase #3	$7.79	9.735%	$8.5484	$8.55	$8.55	$8.50
Purchase #4	$137.81	10.497%	$152.2759	$152.28	$152.30	$152.30
Purchase #5	$37.53	6.434%	$39.9447	$39.94	$39.95	$39.90
Purchase #6	$145.34	3.495%	$150.4196	$150.42	$150.40	$150.40
Purchase #7	$94.46	11.378%	$105.2077	$105.21	$105.20	$105.20
7 purchase totals =	$670.07		$721.6010	$721.61	$721.60	$721.50