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	$126.93	11.493%	$141.5181	$141.52	$141.50	$141.50
Purchase #2	$39.92	8.852%	$43.4537	$43.45	$43.45	$43.50
Purchase #3	$73.78	13.778%	$83.9454	$83.95	$83.95	$83.90
Purchase #4	$190.44	12.777%	$214.7725	$214.77	$214.75	$214.80
Purchase #5	$249.27	7.180%	$267.1676	$267.17	$267.15	$267.20
Purchase #6	$249.27	11.152%	$277.0686	$277.07	$277.05	$277.10
Purchase #7	$239.88	13.524%	$272.3214	$272.32	$272.30	$272.30
7 purchase totals =	$1,169.49		$1,300.2473	$1,300.25	$1,300.15	$1,300.30