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	$29.95	9.454%	$32.7815	$32.78	$32.80	$32.80
Purchase #2	$31.34	13.110%	$35.4487	$35.45	$35.45	$35.40
Purchase #3	$104.40	6.423%	$111.1056	$111.11	$111.10	$111.10
Purchase #4	$199.29	3.600%	$206.4644	$206.46	$206.45	$206.50
Purchase #5	$99.65	9.805%	$109.4207	$109.42	$109.40	$109.40
Purchase #6	$10.31	9.328%	$11.2717	$11.27	$11.25	$11.30
Purchase #7	$35.99	8.715%	$39.1265	$39.13	$39.15	$39.10
7 purchase totals =	$510.93		$545.6191	$545.62	$545.60	$545.60