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	$228.43	11.632%	$255.001	$255.00	$255.00	$255.00
Purchase #2	$34.33	13.231%	$38.8722	$38.87	$38.85	$38.90
Purchase #3	$179.81	4.254%	$187.4591	$187.46	$187.45	$187.50
Purchase #4	$73.56	8.485%	$79.8016	$79.80	$79.80	$79.80
Purchase #5	$91.52	7.514%	$98.3968	$98.40	$98.40	$98.40
Purchase #6	$152.81	13.226%	$173.0207	$173.02	$173.00	$173.00
Purchase #7	$94.41	6.547%	$100.591	$100.59	$100.60	$100.60
7 purchase totals =	$854.87		$933.1424	$933.14	$933.10	$933.20