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	$81.81	10.714%	$90.5751	$90.58	$90.60	$90.60
Purchase #2	$206.35	3.750%	$214.0881	$214.09	$214.10	$214.10
Purchase #3	$58.35	4.738%	$61.1146	$61.11	$61.10	$61.10
Purchase #4	$40.34	12.524%	$45.3922	$45.39	$45.40	$45.40
Purchase #5	$224.96	6.752%	$240.1493	$240.15	$240.15	$240.10
Purchase #6	$102.49	3.341%	$105.9142	$105.91	$105.90	$105.90
Purchase #7	$158.93	3.406%	$164.3432	$164.34	$164.35	$164.30
7 purchase totals =	$873.23		$921.5767	$921.57	$921.60	$921.50