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	$229.87	8.617%	$249.6779	$249.68	$249.70	$249.70
Purchase #2	$125.48	3.766%	$130.2056	$130.21	$130.20	$130.20
Purchase #3	$127.77	11.588%	$142.576	$142.58	$142.60	$142.60
Purchase #4	$163.64	6.200%	$173.7857	$173.79	$173.80	$173.80
Purchase #5	$91.32	9.518%	$100.0118	$100.01	$100.00	$100.00
Purchase #6	$57.32	13.418%	$65.0112	$65.01	$65.00	$65.00
Purchase #7	$204.28	10.447%	$225.6211	$225.62	$225.60	$225.60
7 purchase totals =	$999.68		$1,086.8893	$1,086.90	$1,086.90	$1,086.90