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	$6.89	4.396%	$7.1929	$7.19	$7.20	$7.20
Purchase #2	$202.56	6.416%	$215.5562	$215.56	$215.55	$215.60
Purchase #3	$176.54	4.635%	$184.7226	$184.72	$184.70	$184.70
Purchase #4	$130.92	5.246%	$137.7881	$137.79	$137.80	$137.80
Purchase #5	$79.56	3.557%	$82.3899	$82.39	$82.40	$82.40
Purchase #6	$185.70	9.241%	$202.8605	$202.86	$202.85	$202.90
Purchase #7	$163.71	5.733%	$173.0955	$173.10	$173.10	$173.10
7 purchase totals =	$945.88		$1,003.6057	$1,003.61	$1,003.60	$1,003.70