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	$120.25	6.177%	$127.6778	$127.68	$127.70	$127.70
Purchase #2	$68.76	10.566%	$76.0252	$76.03	$76.05	$76.00
Purchase #3	$19.98	9.282%	$21.8345	$21.83	$21.85	$21.80
Purchase #4	$182.91	12.235%	$205.289	$205.29	$205.30	$205.30
Purchase #5	$230.27	7.865%	$248.3807	$248.38	$248.40	$248.40
Purchase #6	$22.61	11.694%	$25.254	$25.25	$25.25	$25.30
Purchase #7	$105.43	5.627%	$111.3625	$111.36	$111.35	$111.40
7 purchase totals =	$750.21		$815.8237	$815.82	$815.90	$815.90