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	$18.66	11.545%	$20.8143	$20.81	$20.80	$20.80
Purchase #2	$29.83	12.802%	$33.6488	$33.65	$33.65	$33.60
Purchase #3	$172.71	13.768%	$196.4887	$196.49	$196.50	$196.50
Purchase #4	$240.77	8.746%	$261.8277	$261.83	$261.85	$261.80
Purchase #5	$24.56	10.336%	$27.0985	$27.10	$27.10	$27.10
Purchase #6	$107.75	4.112%	$112.1807	$112.18	$112.20	$112.20
Purchase #7	$103.85	10.111%	$114.3503	$114.35	$114.35	$114.40
7 purchase totals =	$698.13		$766.4090	$766.41	$766.45	$766.40