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	$166.89	5.520%	$176.1023	$176.10	$176.10	$176.10
Purchase #2	$47.61	6.190%	$50.5571	$50.56	$50.55	$50.60
Purchase #3	$215.39	10.521%	$238.0512	$238.05	$238.05	$238.10
Purchase #4	$42.57	6.634%	$45.3941	$45.39	$45.40	$45.40
Purchase #5	$89.56	13.798%	$101.9175	$101.92	$101.90	$101.90
Purchase #6	$80.59	13.491%	$91.4624	$91.46	$91.45	$91.50
Purchase #7	$21.82	10.714%	$24.1578	$24.16	$24.15	$24.20
7 purchase totals =	$664.43		$727.6424	$727.64	$727.60	$727.80