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	$74.67	10.382%	$82.4222	$82.42	$82.40	$82.40
Purchase #2	$137.36	12.491%	$154.5176	$154.52	$154.50	$154.50
Purchase #3	$129.47	5.725%	$136.8822	$136.88	$136.90	$136.90
Purchase #4	$37.26	3.131%	$38.4266	$38.43	$38.45	$38.40
Purchase #5	$188.44	11.213%	$209.5698	$209.57	$209.55	$209.60
Purchase #6	$41.30	7.856%	$44.5445	$44.54	$44.55	$44.50
Purchase #7	$145.54	4.561%	$152.1781	$152.18	$152.20	$152.20
7 purchase totals =	$754.04		$818.5410	$818.54	$818.55	$818.50