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	$59.68	11.310%	$66.4298	$66.43	$66.45	$66.40
Purchase #2	$209.38	6.784%	$223.5843	$223.58	$223.60	$223.60
Purchase #3	$229.98	12.848%	$259.5278	$259.53	$259.55	$259.50
Purchase #4	$85.41	5.696%	$90.275	$90.28	$90.30	$90.30
Purchase #5	$30.32	11.447%	$33.7907	$33.79	$33.80	$33.80
Purchase #6	$18.95	4.410%	$19.7857	$19.79	$19.80	$19.80
Purchase #7	$183.78	7.368%	$197.3209	$197.32	$197.30	$197.30
7 purchase totals =	$817.50		$890.7142	$890.72	$890.80	$890.70