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	$41.64	6.617%	$44.3953	$44.40	$44.40	$44.40
Purchase #2	$119.35	7.629%	$128.4552	$128.46	$128.45	$128.50
Purchase #3	$250.54	4.580%	$262.0147	$262.01	$262.00	$262.00
Purchase #4	$108.82	7.375%	$116.8455	$116.85	$116.85	$116.80
Purchase #5	$182.96	8.544%	$198.5921	$198.59	$198.60	$198.60
Purchase #6	$137.91	5.578%	$145.6026	$145.60	$145.60	$145.60
Purchase #7	$128.30	12.485%	$144.3183	$144.32	$144.30	$144.30
7 purchase totals =	$969.52		$1,040.2237	$1,040.23	$1,040.20	$1,040.20