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	$89.98	11.805%	$100.6021	$100.60	$100.60	$100.60
Purchase #2	$229.62	3.374%	$237.3674	$237.37	$237.35	$237.40
Purchase #3	$19.69	5.694%	$20.8111	$20.81	$20.80	$20.80
Purchase #4	$19.47	11.663%	$21.7408	$21.74	$21.75	$21.70
Purchase #5	$127.31	9.233%	$139.0645	$139.06	$139.05	$139.10
Purchase #6	$61.89	6.410%	$65.8571	$65.86	$65.85	$65.90
Purchase #7	$43.31	5.390%	$45.6444	$45.64	$45.65	$45.60
7 purchase totals =	$591.27		$631.0874	$631.08	$631.05	$631.10