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	$24.60	10.712%	$27.2352	$27.24	$27.25	$27.20
Purchase #2	$93.45	12.468%	$105.1013	$105.10	$105.10	$105.10
Purchase #3	$48.31	5.869%	$51.1453	$51.15	$51.15	$51.10
Purchase #4	$101.65	10.685%	$112.5113	$112.51	$112.50	$112.50
Purchase #5	$246.37	13.679%	$280.071	$280.07	$280.05	$280.10
Purchase #6	$93.38	11.820%	$104.4175	$104.42	$104.40	$104.40
Purchase #7	$223.34	8.718%	$242.8108	$242.81	$242.80	$242.80
7 purchase totals =	$831.10		$923.2924	$923.30	$923.25	$923.20