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	$48.31	4.139%	$50.3096	$50.31	$50.30	$50.30
Purchase #2	$80.99	6.778%	$86.4795	$86.48	$86.50	$86.50
Purchase #3	$54.28	5.169%	$57.0857	$57.09	$57.10	$57.10
Purchase #4	$138.69	12.804%	$156.4479	$156.45	$156.45	$156.40
Purchase #5	$202.51	12.448%	$227.7184	$227.72	$227.70	$227.70
Purchase #6	$207.97	8.462%	$225.5684	$225.57	$225.55	$225.60
Purchase #7	$111.98	10.275%	$123.4859	$123.49	$123.50	$123.50
7 purchase totals =	$844.73		$927.0954	$927.11	$927.10	$927.10