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	$51.91	13.618%	$58.9791	$58.98	$59.00	$59.00
Purchase #2	$105.62	7.284%	$113.3134	$113.31	$113.30	$113.30
Purchase #3	$41.58	11.249%	$46.2573	$46.26	$46.25	$46.30
Purchase #4	$75.42	9.535%	$82.6113	$82.61	$82.60	$82.60
Purchase #5	$45.91	10.665%	$50.8063	$50.81	$50.80	$50.80
Purchase #6	$14.30	11.713%	$15.975	$15.98	$16.00	$16.00
Purchase #7	$30.41	10.621%	$33.6398	$33.64	$33.65	$33.60
7 purchase totals =	$365.15		$401.5822	$401.59	$401.60	$401.60