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	$121.85	8.188%	$131.8271	$131.83	$131.85	$131.80
Purchase #2	$134.61	3.746%	$139.6525	$139.65	$139.65	$139.70
Purchase #3	$37.83	7.787%	$40.7758	$40.78	$40.80	$40.80
Purchase #4	$107.68	5.622%	$113.7338	$113.73	$113.75	$113.70
Purchase #5	$144.28	7.745%	$155.4545	$155.45	$155.45	$155.50
Purchase #6	$67.65	11.446%	$75.3932	$75.39	$75.40	$75.40
Purchase #7	$127.41	10.338%	$140.5816	$140.58	$140.60	$140.60
7 purchase totals =	$741.31		$797.4185	$797.41	$797.50	$797.50