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	$58.68	12.758%	$66.1664	$66.17	$66.15	$66.20
Purchase #2	$98.39	9.132%	$107.375	$107.38	$107.40	$107.40
Purchase #3	$102.33	5.856%	$108.3224	$108.32	$108.30	$108.30
Purchase #4	$77.73	3.593%	$80.5228	$80.52	$80.50	$80.50
Purchase #5	$192.57	8.672%	$209.2697	$209.27	$209.25	$209.30
Purchase #6	$42.90	12.518%	$48.2702	$48.27	$48.25	$48.30
Purchase #7	$153.59	8.466%	$166.5929	$166.59	$166.60	$166.60
7 purchase totals =	$726.19		$786.5194	$786.52	$786.45	$786.60