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	$42.28	11.462%	$47.1261	$47.13	$47.15	$47.10
Purchase #2	$35.49	6.743%	$37.8831	$37.88	$37.90	$37.90
Purchase #3	$200.84	7.732%	$216.3689	$216.37	$216.35	$216.40
Purchase #4	$47.91	13.287%	$54.2758	$54.28	$54.30	$54.30
Purchase #5	$105.32	11.794%	$117.7414	$117.74	$117.75	$117.70
Purchase #6	$35.92	9.534%	$39.3446	$39.34	$39.35	$39.30
Purchase #7	$132.95	13.625%	$151.0644	$151.06	$151.05	$151.10
7 purchase totals =	$600.71		$663.8043	$663.80	$663.85	$663.80