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	$120.52	10.283%	$132.9131	$132.91	$132.90	$132.90
Purchase #2	$144.29	7.326%	$154.8607	$154.86	$154.85	$154.90
Purchase #3	$72.83	9.738%	$79.9222	$79.92	$79.90	$79.90
Purchase #4	$45.70	9.406%	$49.9985	$50.00	$50.00	$50.00
Purchase #5	$243.95	10.522%	$269.6184	$269.62	$269.60	$269.60
Purchase #6	$103.65	6.426%	$110.3105	$110.31	$110.30	$110.30
Purchase #7	$103.37	7.438%	$111.0587	$111.06	$111.05	$111.10
7 purchase totals =	$834.31		$908.6821	$908.68	$908.60	$908.70