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	$34.37	8.745%	$37.3757	$37.38	$37.40	$37.40
Purchase #2	$141.70	10.253%	$156.2285	$156.23	$156.25	$156.20
Purchase #3	$53.86	9.815%	$59.1464	$59.15	$59.15	$59.10
Purchase #4	$19.42	11.390%	$21.6319	$21.63	$21.65	$21.60
Purchase #5	$245.69	13.180%	$278.0719	$278.07	$278.05	$278.10
Purchase #6	$213.56	8.209%	$231.0911	$231.09	$231.10	$231.10
Purchase #7	$138.60	10.502%	$153.1558	$153.16	$153.15	$153.20
7 purchase totals =	$847.20		$936.7013	$936.71	$936.75	$936.70