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	$178.94	13.392%	$202.9036	$202.90	$202.90	$202.90
Purchase #2	$241.29	7.628%	$259.6956	$259.70	$259.70	$259.70
Purchase #3	$18.50	10.374%	$20.4192	$20.42	$20.40	$20.40
Purchase #4	$112.89	12.617%	$127.1333	$127.13	$127.15	$127.10
Purchase #5	$124.88	9.760%	$137.0683	$137.07	$137.05	$137.10
Purchase #6	$79.45	13.631%	$90.2798	$90.28	$90.30	$90.30
Purchase #7	$63.94	5.824%	$67.6639	$67.66	$67.65	$67.70
7 purchase totals =	$819.89		$905.1637	$905.16	$905.15	$905.20