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	$82.72	9.838%	$90.858	$90.86	$90.85	$90.90
Purchase #2	$169.31	4.153%	$176.3414	$176.34	$176.35	$176.30
Purchase #3	$124.77	5.867%	$132.0903	$132.09	$132.10	$132.10
Purchase #4	$176.96	6.699%	$188.8146	$188.81	$188.80	$188.80
Purchase #5	$52.50	9.298%	$57.3815	$57.38	$57.40	$57.40
Purchase #6	$36.82	7.784%	$39.6861	$39.69	$39.70	$39.70
Purchase #7	$113.62	4.106%	$118.2852	$118.29	$118.30	$118.30
7 purchase totals =	$756.70		$803.4571	$803.46	$803.50	$803.50