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	$29.28	10.638%	$32.3948	$32.39	$32.40	$32.40
Purchase #2	$5.76	5.118%	$6.0548	$6.05	$6.05	$6.10
Purchase #3	$45.30	9.658%	$49.6751	$49.68	$49.70	$49.70
Purchase #4	$188.54	11.721%	$210.6388	$210.64	$210.65	$210.60
Purchase #5	$48.26	10.462%	$53.309	$53.31	$53.30	$53.30
Purchase #6	$76.77	11.295%	$85.4412	$85.44	$85.45	$85.40
Purchase #7	$99.59	11.806%	$111.3476	$111.35	$111.35	$111.30
7 purchase totals =	$493.50		$548.8613	$548.86	$548.90	$548.80