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	$158.25	9.848%	$173.8345	$173.83	$173.85	$173.80
Purchase #2	$242.31	3.305%	$250.3183	$250.32	$250.30	$250.30
Purchase #3	$246.91	12.675%	$278.2058	$278.21	$278.20	$278.20
Purchase #4	$29.50	6.409%	$31.3907	$31.39	$31.40	$31.40
Purchase #5	$66.41	5.611%	$70.1363	$70.14	$70.15	$70.10
Purchase #6	$231.79	8.587%	$251.6938	$251.69	$251.70	$251.70
Purchase #7	$81.60	10.664%	$90.3018	$90.30	$90.30	$90.30
7 purchase totals =	$1,056.77		$1,145.8812	$1,145.88	$1,145.90	$1,145.80