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	$107.78	4.194%	$112.3003	$112.30	$112.30	$112.30
Purchase #2	$196.69	3.401%	$203.3794	$203.38	$203.40	$203.40
Purchase #3	$40.34	13.116%	$45.631	$45.63	$45.65	$45.60
Purchase #4	$44.99	8.516%	$48.8213	$48.82	$48.80	$48.80
Purchase #5	$21.61	8.308%	$23.4054	$23.41	$23.40	$23.40
Purchase #6	$127.39	10.386%	$140.6207	$140.62	$140.60	$140.60
Purchase #7	$24.48	11.477%	$27.2896	$27.29	$27.30	$27.30
7 purchase totals =	$563.28		$601.4477	$601.45	$601.45	$601.40