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	$209.59	12.376%	$235.5289	$235.53	$235.55	$235.50
Purchase #2	$239.28	10.357%	$264.0622	$264.06	$264.05	$264.10
Purchase #3	$173.60	4.528%	$181.4606	$181.46	$181.45	$181.50
Purchase #4	$51.99	3.487%	$53.8029	$53.80	$53.80	$53.80
Purchase #5	$142.57	6.238%	$151.4635	$151.46	$151.45	$151.50
Purchase #6	$67.36	4.396%	$70.3211	$70.32	$70.30	$70.30
Purchase #7	$32.83	6.280%	$34.8917	$34.89	$34.90	$34.90
7 purchase totals =	$917.22		$991.5309	$991.52	$991.50	$991.60