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	$247.37	6.635%	$263.783	$263.78	$263.80	$263.80
Purchase #2	$210.61	13.182%	$238.3726	$238.37	$238.35	$238.40
Purchase #3	$207.88	7.552%	$223.5791	$223.58	$223.60	$223.60
Purchase #4	$72.74	12.866%	$82.0987	$82.10	$82.10	$82.10
Purchase #5	$179.87	13.786%	$204.6669	$204.67	$204.65	$204.70
Purchase #6	$34.70	8.388%	$37.6106	$37.61	$37.60	$37.60
Purchase #7	$122.41	8.298%	$132.5676	$132.57	$132.55	$132.60
7 purchase totals =	$1,075.58		$1,182.6785	$1,182.68	$1,182.65	$1,182.80