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	$123.88	3.838%	$128.6345	$128.63	$128.65	$128.60
Purchase #2	$158.73	11.138%	$176.4093	$176.41	$176.40	$176.40
Purchase #3	$158.48	5.649%	$167.4325	$167.43	$167.45	$167.40
Purchase #4	$153.28	8.667%	$166.5648	$166.56	$166.55	$166.60
Purchase #5	$246.37	7.583%	$265.0522	$265.05	$265.05	$265.10
Purchase #6	$219.94	8.632%	$238.9252	$238.93	$238.95	$238.90
Purchase #7	$105.68	7.420%	$113.5215	$113.52	$113.50	$113.50
7 purchase totals =	$1,166.36		$1,256.5400	$1,256.53	$1,256.55	$1,256.50