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	$83.32	3.223%	$86.0054	$86.01	$86.00	$86.00
Purchase #2	$33.72	13.649%	$38.3224	$38.32	$38.30	$38.30
Purchase #3	$100.45	5.633%	$106.1083	$106.11	$106.10	$106.10
Purchase #4	$54.60	4.861%	$57.2541	$57.25	$57.25	$57.30
Purchase #5	$18.38	12.403%	$20.6597	$20.66	$20.65	$20.70
Purchase #6	$13.64	9.727%	$14.9668	$14.97	$14.95	$15.00
Purchase #7	$196.69	13.145%	$222.5449	$222.54	$222.55	$222.50
7 purchase totals =	$500.80		$545.8616	$545.86	$545.80	$545.90