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	$145.96	12.699%	$164.4955	$164.50	$164.50	$164.50
Purchase #2	$209.68	10.544%	$231.7887	$231.79	$231.80	$231.80
Purchase #3	$126.85	11.336%	$141.2297	$141.23	$141.25	$141.20
Purchase #4	$141.25	5.396%	$148.8719	$148.87	$148.85	$148.90
Purchase #5	$89.87	11.440%	$100.1511	$100.15	$100.15	$100.20
Purchase #6	$201.39	8.708%	$218.927	$218.93	$218.95	$218.90
Purchase #7	$90.77	3.513%	$93.9588	$93.96	$93.95	$94.00
7 purchase totals =	$1,005.77		$1,099.4227	$1,099.43	$1,099.45	$1,099.50