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	$39.95	6.436%	$42.5212	$42.52	$42.50	$42.50
Purchase #2	$26.55	7.432%	$28.5232	$28.52	$28.50	$28.50
Purchase #3	$11.29	6.484%	$12.022	$12.02	$12.00	$12.00
Purchase #4	$132.69	5.295%	$139.7159	$139.72	$139.70	$139.70
Purchase #5	$74.53	10.515%	$82.3668	$82.37	$82.35	$82.40
Purchase #6	$166.33	3.282%	$171.789	$171.79	$171.80	$171.80
Purchase #7	$66.45	11.305%	$73.9622	$73.96	$73.95	$74.00
7 purchase totals =	$517.79		$550.9003	$550.90	$550.80	$550.90