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	$133.89	9.616%	$146.7649	$146.76	$146.75	$146.80
Purchase #2	$64.80	8.596%	$70.3702	$70.37	$70.35	$70.40
Purchase #3	$147.68	4.172%	$153.8412	$153.84	$153.85	$153.80
Purchase #4	$63.81	3.870%	$66.2794	$66.28	$66.30	$66.30
Purchase #5	$85.91	5.244%	$90.4151	$90.42	$90.40	$90.40
Purchase #6	$234.30	4.392%	$244.5905	$244.59	$244.60	$244.60
Purchase #7	$142.96	9.374%	$156.3611	$156.36	$156.35	$156.40
7 purchase totals =	$873.35		$928.6224	$928.62	$928.60	$928.70