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	$14.62	10.156%	$16.1048	$16.10	$16.10	$16.10
Purchase #2	$29.87	9.167%	$32.6082	$32.61	$32.60	$32.60
Purchase #3	$99.83	3.634%	$103.4578	$103.46	$103.45	$103.50
Purchase #4	$47.37	4.132%	$49.3273	$49.33	$49.35	$49.30
Purchase #5	$176.55	7.809%	$190.3368	$190.34	$190.35	$190.30
Purchase #6	$62.93	10.499%	$69.537	$69.54	$69.55	$69.50
Purchase #7	$83.30	8.536%	$90.4105	$90.41	$90.40	$90.40
7 purchase totals =	$514.47		$551.7824	$551.79	$551.80	$551.70