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	$106.83	12.698%	$120.3953	$120.40	$120.40	$120.40
Purchase #2	$33.89	13.562%	$38.4862	$38.49	$38.50	$38.50
Purchase #3	$133.78	9.469%	$146.4476	$146.45	$146.45	$146.40
Purchase #4	$49.91	8.333%	$54.069	$54.07	$54.05	$54.10
Purchase #5	$90.72	11.682%	$101.3179	$101.32	$101.30	$101.30
Purchase #6	$55.64	13.238%	$63.0056	$63.01	$63.00	$63.00
Purchase #7	$247.45	4.467%	$258.5036	$258.50	$258.50	$258.50
7 purchase totals =	$718.22		$782.2252	$782.24	$782.20	$782.20