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	$62.79	5.645%	$66.3345	$66.33	$66.35	$66.30
Purchase #2	$78.44	5.249%	$82.5573	$82.56	$82.55	$82.60
Purchase #3	$103.51	10.184%	$114.0515	$114.05	$114.05	$114.10
Purchase #4	$44.78	8.671%	$48.6629	$48.66	$48.65	$48.70
Purchase #5	$66.34	3.163%	$68.4383	$68.44	$68.45	$68.40
Purchase #6	$91.70	9.692%	$100.5876	$100.59	$100.60	$100.60
Purchase #7	$45.70	9.240%	$49.9227	$49.92	$49.90	$49.90
7 purchase totals =	$493.26		$530.5548	$530.55	$530.55	$530.60