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	$222.77	7.716%	$239.9589	$239.96	$239.95	$240.00
Purchase #2	$60.46	8.265%	$65.457	$65.46	$65.45	$65.50
Purchase #3	$43.52	8.662%	$47.2897	$47.29	$47.30	$47.30
Purchase #4	$85.55	5.552%	$90.2997	$90.30	$90.30	$90.30
Purchase #5	$48.63	11.182%	$54.0678	$54.07	$54.05	$54.10
Purchase #6	$36.69	13.203%	$41.5342	$41.53	$41.55	$41.50
Purchase #7	$160.55	3.649%	$166.4085	$166.41	$166.40	$166.40
7 purchase totals =	$658.17		$705.0158	$705.02	$705.00	$705.10