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	$78.86	12.497%	$88.7151	$88.72	$88.70	$88.70
Purchase #2	$27.93	7.367%	$29.9876	$29.99	$30.00	$30.00
Purchase #3	$231.92	3.437%	$239.8911	$239.89	$239.90	$239.90
Purchase #4	$54.96	9.142%	$59.9844	$59.98	$60.00	$60.00
Purchase #5	$37.54	11.111%	$41.7111	$41.71	$41.70	$41.70
Purchase #6	$78.96	13.237%	$89.4119	$89.41	$89.40	$89.40
Purchase #7	$72.68	6.125%	$77.1317	$77.13	$77.15	$77.10
7 purchase totals =	$582.85		$626.8329	$626.83	$626.85	$626.80