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	$24.89	11.810%	$27.8295	$27.83	$27.85	$27.80
Purchase #2	$143.82	9.545%	$157.5476	$157.55	$157.55	$157.50
Purchase #3	$182.68	7.484%	$196.3518	$196.35	$196.35	$196.40
Purchase #4	$52.47	3.229%	$54.1643	$54.16	$54.15	$54.20
Purchase #5	$56.40	7.806%	$60.8026	$60.80	$60.80	$60.80
Purchase #6	$123.77	7.692%	$133.2904	$133.29	$133.30	$133.30
Purchase #7	$212.45	3.264%	$219.3844	$219.38	$219.40	$219.40
7 purchase totals =	$796.48		$849.3706	$849.36	$849.40	$849.40