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	$79.83	12.461%	$89.7776	$89.78	$89.80	$89.80
Purchase #2	$153.87	13.807%	$175.1148	$175.11	$175.10	$175.10
Purchase #3	$145.48	12.776%	$164.0665	$164.07	$164.05	$164.10
Purchase #4	$210.42	8.577%	$228.4677	$228.47	$228.45	$228.50
Purchase #5	$170.76	11.630%	$190.6194	$190.62	$190.60	$190.60
Purchase #6	$27.47	6.589%	$29.28	$29.28	$29.30	$29.30
Purchase #7	$43.44	4.868%	$45.5547	$45.55	$45.55	$45.60
7 purchase totals =	$831.27		$922.8807	$922.88	$922.85	$923.00