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	$110.67	13.750%	$125.8871	$125.89	$125.90	$125.90
Purchase #2	$173.77	4.547%	$181.6713	$181.67	$181.65	$181.70
Purchase #3	$65.43	10.699%	$72.4304	$72.43	$72.45	$72.40
Purchase #4	$58.86	11.438%	$65.5924	$65.59	$65.60	$65.60
Purchase #5	$125.88	7.142%	$134.8703	$134.87	$134.85	$134.90
Purchase #6	$151.27	11.850%	$169.1955	$169.20	$169.20	$169.20
Purchase #7	$132.81	9.353%	$145.2317	$145.23	$145.25	$145.20
7 purchase totals =	$818.69		$894.8787	$894.88	$894.90	$894.90