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	$169.26	6.541%	$180.3313	$180.33	$180.35	$180.30
Purchase #2	$28.85	8.226%	$31.2232	$31.22	$31.20	$31.20
Purchase #3	$78.32	7.746%	$84.3867	$84.39	$84.40	$84.40
Purchase #4	$127.70	13.415%	$144.831	$144.83	$144.85	$144.80
Purchase #5	$71.86	12.349%	$80.734	$80.73	$80.75	$80.70
Purchase #6	$244.92	10.744%	$271.2342	$271.23	$271.25	$271.20
Purchase #7	$65.51	3.174%	$67.5893	$67.59	$67.60	$67.60
7 purchase totals =	$786.42		$860.3297	$860.32	$860.40	$860.20