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	$39.40	12.757%	$44.4263	$44.43	$44.45	$44.40
Purchase #2	$46.34	8.178%	$50.1297	$50.13	$50.15	$50.10
Purchase #3	$127.78	11.131%	$142.0032	$142.00	$142.00	$142.00
Purchase #4	$39.86	13.774%	$45.3503	$45.35	$45.35	$45.40
Purchase #5	$44.70	7.677%	$48.1316	$48.13	$48.15	$48.10
Purchase #6	$39.42	12.151%	$44.2099	$44.21	$44.20	$44.20
Purchase #7	$212.59	4.577%	$222.3202	$222.32	$222.30	$222.30
7 purchase totals =	$550.09		$596.5712	$596.57	$596.60	$596.50