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	$49.57	10.844%	$54.9454	$54.95	$54.95	$54.90
Purchase #2	$81.26	12.475%	$91.3972	$91.40	$91.40	$91.40
Purchase #3	$70.75	10.678%	$78.3047	$78.30	$78.30	$78.30
Purchase #4	$98.54	6.690%	$105.1323	$105.13	$105.15	$105.10
Purchase #5	$58.79	11.559%	$65.5855	$65.59	$65.60	$65.60
Purchase #6	$167.53	12.346%	$188.2133	$188.21	$188.20	$188.20
Purchase #7	$12.60	8.136%	$13.6251	$13.63	$13.65	$13.60
7 purchase totals =	$539.04		$597.2035	$597.21	$597.25	$597.10