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	$234.32	10.513%	$258.9541	$258.95	$258.95	$259.00
Purchase #2	$37.45	13.705%	$42.5825	$42.58	$42.60	$42.60
Purchase #3	$21.49	5.849%	$22.747	$22.75	$22.75	$22.70
Purchase #4	$66.94	8.289%	$72.4887	$72.49	$72.50	$72.50
Purchase #5	$120.47	8.382%	$130.5678	$130.57	$130.55	$130.60
Purchase #6	$162.38	3.771%	$168.5033	$168.50	$168.50	$168.50
Purchase #7	$34.41	13.339%	$38.9999	$39.00	$39.00	$39.00
7 purchase totals =	$677.46		$734.8433	$734.84	$734.85	$734.90