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	$110.49	11.528%	$123.2273	$123.23	$123.25	$123.20
Purchase #2	$149.29	8.127%	$161.4228	$161.42	$161.40	$161.40
Purchase #3	$150.68	3.412%	$155.8212	$155.82	$155.80	$155.80
Purchase #4	$94.25	12.716%	$106.2348	$106.23	$106.25	$106.20
Purchase #5	$198.90	10.599%	$219.9814	$219.98	$220.00	$220.00
Purchase #6	$63.98	13.178%	$72.4113	$72.41	$72.40	$72.40
Purchase #7	$26.89	5.869%	$28.4682	$28.47	$28.45	$28.50
7 purchase totals =	$794.48		$867.5670	$867.56	$867.55	$867.50