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	$42.97	3.351%	$44.4099	$44.41	$44.40	$44.40
Purchase #2	$22.52	9.379%	$24.6322	$24.63	$24.65	$24.60
Purchase #3	$123.31	5.660%	$130.2893	$130.29	$130.30	$130.30
Purchase #4	$124.97	4.243%	$130.2725	$130.27	$130.25	$130.30
Purchase #5	$39.26	13.619%	$44.6068	$44.61	$44.60	$44.60
Purchase #6	$38.54	4.307%	$40.1999	$40.20	$40.20	$40.20
Purchase #7	$241.34	5.734%	$255.1784	$255.18	$255.20	$255.20
7 purchase totals =	$632.91		$669.5890	$669.59	$669.60	$669.60