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	$229.36	11.376%	$255.452	$255.45	$255.45	$255.50
Purchase #2	$150.77	7.783%	$162.5044	$162.50	$162.50	$162.50
Purchase #3	$170.49	3.542%	$176.5288	$176.53	$176.55	$176.50
Purchase #4	$223.25	6.874%	$238.5962	$238.60	$238.60	$238.60
Purchase #5	$200.54	8.504%	$217.5939	$217.59	$217.60	$217.60
Purchase #6	$122.90	12.600%	$138.3854	$138.39	$138.40	$138.40
Purchase #7	$58.95	12.713%	$66.4443	$66.44	$66.45	$66.40
7 purchase totals =	$1,156.26		$1,255.5050	$1,255.50	$1,255.55	$1,255.50