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	$152.49	4.142%	$158.8061	$158.81	$158.80	$158.80
Purchase #2	$37.85	13.831%	$43.085	$43.09	$43.10	$43.10
Purchase #3	$16.44	9.523%	$18.0056	$18.01	$18.00	$18.00
Purchase #4	$79.29	11.368%	$88.3037	$88.30	$88.30	$88.30
Purchase #5	$98.41	13.290%	$111.4887	$111.49	$111.50	$111.50
Purchase #6	$125.59	11.204%	$139.6611	$139.66	$139.65	$139.70
Purchase #7	$102.36	8.617%	$111.1804	$111.18	$111.20	$111.20
7 purchase totals =	$612.43		$670.5306	$670.54	$670.55	$670.60