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	$60.37	9.801%	$66.2869	$66.29	$66.30	$66.30
Purchase #2	$146.76	12.682%	$165.3721	$165.37	$165.35	$165.40
Purchase #3	$156.68	5.852%	$165.8489	$165.85	$165.85	$165.80
Purchase #4	$250.56	11.687%	$279.8429	$279.84	$279.85	$279.80
Purchase #5	$25.49	11.246%	$28.3566	$28.36	$28.35	$28.40
Purchase #6	$37.41	6.290%	$39.7631	$39.76	$39.75	$39.80
Purchase #7	$104.42	9.702%	$114.5508	$114.55	$114.55	$114.60
7 purchase totals =	$781.69		$860.0213	$860.02	$860.00	$860.10