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	$100.96	10.198%	$111.2559	$111.26	$111.25	$111.30
Purchase #2	$15.25	4.113%	$15.8772	$15.88	$15.90	$15.90
Purchase #3	$221.43	5.232%	$233.0152	$233.02	$233.00	$233.00
Purchase #4	$248.31	11.776%	$277.551	$277.55	$277.55	$277.60
Purchase #5	$100.64	8.343%	$109.0364	$109.04	$109.05	$109.00
Purchase #6	$9.59	10.308%	$10.5785	$10.58	$10.60	$10.60
Purchase #7	$35.58	13.413%	$40.3523	$40.35	$40.35	$40.40
7 purchase totals =	$731.76		$797.6665	$797.68	$797.70	$797.80