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	$132.86	6.334%	$141.2754	$141.28	$141.30	$141.30
Purchase #2	$81.28	11.707%	$90.7954	$90.80	$90.80	$90.80
Purchase #3	$46.99	11.837%	$52.5522	$52.55	$52.55	$52.60
Purchase #4	$150.54	7.244%	$161.4451	$161.45	$161.45	$161.40
Purchase #5	$92.51	9.355%	$101.1643	$101.16	$101.15	$101.20
Purchase #6	$222.91	11.488%	$248.5179	$248.52	$248.50	$248.50
Purchase #7	$113.77	8.587%	$123.5394	$123.54	$123.55	$123.50
7 purchase totals =	$840.86		$919.2897	$919.30	$919.30	$919.30