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	$25.92	6.643%	$27.6419	$27.64	$27.65	$27.60
Purchase #2	$40.35	10.544%	$44.6045	$44.60	$44.60	$44.60
Purchase #3	$250.95	11.356%	$279.4479	$279.45	$279.45	$279.40
Purchase #4	$103.38	13.738%	$117.5823	$117.58	$117.60	$117.60
Purchase #5	$234.48	11.486%	$261.4124	$261.41	$261.40	$261.40
Purchase #6	$72.47	13.549%	$82.289	$82.29	$82.30	$82.30
Purchase #7	$82.27	8.845%	$89.5468	$89.55	$89.55	$89.50
7 purchase totals =	$809.82		$902.5248	$902.52	$902.55	$902.40