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	$151.33	10.634%	$167.4224	$167.42	$167.40	$167.40
Purchase #2	$183.39	11.448%	$204.3845	$204.38	$204.40	$204.40
Purchase #3	$113.42	9.842%	$124.5828	$124.58	$124.60	$124.60
Purchase #4	$40.82	3.635%	$42.3038	$42.30	$42.30	$42.30
Purchase #5	$130.91	6.187%	$139.0094	$139.01	$139.00	$139.00
Purchase #6	$216.68	13.277%	$245.4486	$245.45	$245.45	$245.40
Purchase #7	$151.68	9.500%	$166.0896	$166.09	$166.10	$166.10
7 purchase totals =	$988.23		$1,089.2411	$1,089.23	$1,089.25	$1,089.20