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	$148.85	4.826%	$156.0335	$156.03	$156.05	$156.00
Purchase #2	$221.76	8.580%	$240.787	$240.79	$240.80	$240.80
Purchase #3	$110.59	3.856%	$114.8544	$114.85	$114.85	$114.90
Purchase #4	$87.43	3.707%	$90.671	$90.67	$90.65	$90.70
Purchase #5	$29.72	10.779%	$32.9235	$32.92	$32.90	$32.90
Purchase #6	$48.37	6.680%	$51.6011	$51.60	$51.60	$51.60
Purchase #7	$45.66	5.500%	$48.1713	$48.17	$48.15	$48.20
7 purchase totals =	$692.38		$735.0418	$735.03	$735.00	$735.10