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	$140.31	8.264%	$151.9052	$151.91	$151.90	$151.90
Purchase #2	$166.28	11.618%	$185.5984	$185.60	$185.60	$185.60
Purchase #3	$117.83	13.776%	$134.0623	$134.06	$134.05	$134.10
Purchase #4	$228.32	12.211%	$256.2002	$256.20	$256.20	$256.20
Purchase #5	$163.86	5.230%	$172.4299	$172.43	$172.45	$172.40
Purchase #6	$176.61	4.390%	$184.3632	$184.36	$184.35	$184.40
Purchase #7	$234.97	6.123%	$249.3572	$249.36	$249.35	$249.40
7 purchase totals =	$1,228.18		$1,333.9164	$1,333.92	$1,333.90	$1,334.00