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	$10.58	9.285%	$11.5624	$11.56	$11.55	$11.60
Purchase #2	$35.61	8.535%	$38.6493	$38.65	$38.65	$38.60
Purchase #3	$93.94	5.536%	$99.1405	$99.14	$99.15	$99.10
Purchase #4	$95.57	10.611%	$105.7109	$105.71	$105.70	$105.70
Purchase #5	$70.52	9.736%	$77.3858	$77.39	$77.40	$77.40
Purchase #6	$250.45	6.339%	$266.326	$266.33	$266.35	$266.30
Purchase #7	$82.77	3.122%	$85.3541	$85.35	$85.35	$85.40
7 purchase totals =	$639.44		$684.1290	$684.13	$684.15	$684.10