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	$138.69	8.605%	$150.6243	$150.62	$150.60	$150.60
Purchase #2	$92.83	11.246%	$103.2697	$103.27	$103.25	$103.30
Purchase #3	$39.59	9.401%	$43.3119	$43.31	$43.30	$43.30
Purchase #4	$78.28	13.290%	$88.6834	$88.68	$88.70	$88.70
Purchase #5	$108.94	9.418%	$119.2	$119.20	$119.20	$119.20
Purchase #6	$34.60	13.156%	$39.152	$39.15	$39.15	$39.20
Purchase #7	$42.68	9.113%	$46.5694	$46.57	$46.55	$46.60
7 purchase totals =	$535.61		$590.8107	$590.80	$590.75	$590.90