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	$13.72	4.307%	$14.3109	$14.31	$14.30	$14.30
Purchase #2	$51.91	3.183%	$53.5623	$53.56	$53.55	$53.60
Purchase #3	$165.64	4.500%	$173.0938	$173.09	$173.10	$173.10
Purchase #4	$188.38	6.858%	$201.2991	$201.30	$201.30	$201.30
Purchase #5	$85.35	5.590%	$90.1211	$90.12	$90.10	$90.10
Purchase #6	$154.90	12.225%	$173.8365	$173.84	$173.85	$173.80
Purchase #7	$97.74	12.160%	$109.6252	$109.63	$109.65	$109.60
7 purchase totals =	$757.64		$815.8489	$815.85	$815.85	$815.80