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	$214.46	11.456%	$239.0285	$239.03	$239.05	$239.00
Purchase #2	$33.41	13.186%	$37.8154	$37.82	$37.80	$37.80
Purchase #3	$133.50	3.457%	$138.1151	$138.12	$138.10	$138.10
Purchase #4	$40.35	6.664%	$43.0389	$43.04	$43.05	$43.00
Purchase #5	$210.78	6.492%	$224.4638	$224.46	$224.45	$224.50
Purchase #6	$38.27	10.200%	$42.1735	$42.17	$42.15	$42.20
Purchase #7	$230.44	10.157%	$253.8458	$253.85	$253.85	$253.80
7 purchase totals =	$901.21		$978.4810	$978.49	$978.45	$978.40