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	$29.39	9.826%	$32.2779	$32.28	$32.30	$32.30
Purchase #2	$194.75	9.468%	$213.1889	$213.19	$213.20	$213.20
Purchase #3	$177.42	7.242%	$190.2688	$190.27	$190.25	$190.30
Purchase #4	$67.65	4.761%	$70.8708	$70.87	$70.85	$70.90
Purchase #5	$134.37	7.557%	$144.5243	$144.52	$144.50	$144.50
Purchase #6	$113.96	11.813%	$127.4221	$127.42	$127.40	$127.40
Purchase #7	$41.83	5.448%	$44.1089	$44.11	$44.10	$44.10
7 purchase totals =	$759.37		$822.6617	$822.66	$822.60	$822.70