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	$133.37	4.255%	$139.0449	$139.04	$139.05	$139.00
Purchase #2	$241.64	8.760%	$262.8077	$262.81	$262.80	$262.80
Purchase #3	$117.38	8.169%	$126.9688	$126.97	$126.95	$127.00
Purchase #4	$248.98	8.550%	$270.2678	$270.27	$270.25	$270.30
Purchase #5	$107.41	3.418%	$111.0813	$111.08	$111.10	$111.10
Purchase #6	$99.27	10.576%	$109.7688	$109.77	$109.75	$109.80
Purchase #7	$205.49	8.241%	$222.4244	$222.42	$222.40	$222.40
7 purchase totals =	$1,153.54		$1,242.3637	$1,242.36	$1,242.30	$1,242.40