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	$120.49	13.852%	$137.1803	$137.18	$137.20	$137.20
Purchase #2	$54.82	5.577%	$57.8773	$57.88	$57.90	$57.90
Purchase #3	$45.51	4.144%	$47.3959	$47.40	$47.40	$47.40
Purchase #4	$158.38	4.115%	$164.8973	$164.90	$164.90	$164.90
Purchase #5	$102.62	4.715%	$107.4585	$107.46	$107.45	$107.50
Purchase #6	$93.33	10.730%	$103.3443	$103.34	$103.35	$103.30
Purchase #7	$64.62	12.712%	$72.8345	$72.83	$72.85	$72.80
7 purchase totals =	$639.77		$690.9881	$690.99	$691.05	$691.00