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	$8.59	9.541%	$9.4096	$9.41	$9.40	$9.40
Purchase #2	$82.63	8.769%	$89.8758	$89.88	$89.90	$89.90
Purchase #3	$100.30	10.592%	$110.9238	$110.92	$110.90	$110.90
Purchase #4	$85.85	4.836%	$90.0017	$90.00	$90.00	$90.00
Purchase #5	$150.60	8.695%	$163.6947	$163.69	$163.70	$163.70
Purchase #6	$138.81	3.475%	$143.6336	$143.63	$143.65	$143.60
Purchase #7	$138.43	4.643%	$144.8573	$144.86	$144.85	$144.90
7 purchase totals =	$705.21		$752.3965	$752.39	$752.40	$752.40