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	$54.59	13.345%	$61.875	$61.88	$61.90	$61.90
Purchase #2	$124.65	10.727%	$138.0212	$138.02	$138.00	$138.00
Purchase #3	$81.52	7.725%	$87.8174	$87.82	$87.80	$87.80
Purchase #4	$121.84	8.189%	$131.8175	$131.82	$131.80	$131.80
Purchase #5	$131.50	10.727%	$145.606	$145.61	$145.60	$145.60
Purchase #6	$155.40	12.704%	$175.142	$175.14	$175.15	$175.10
Purchase #7	$204.50	5.214%	$215.1626	$215.16	$215.15	$215.20
7 purchase totals =	$874.00		$955.4417	$955.45	$955.40	$955.40