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	$66.79	6.105%	$70.8675	$70.87	$70.85	$70.90
Purchase #2	$218.79	12.857%	$246.9198	$246.92	$246.90	$246.90
Purchase #3	$127.58	8.591%	$138.5404	$138.54	$138.55	$138.50
Purchase #4	$34.55	12.640%	$38.9171	$38.92	$38.90	$38.90
Purchase #5	$228.72	5.628%	$241.5924	$241.59	$241.60	$241.60
Purchase #6	$122.89	9.824%	$134.9627	$134.96	$134.95	$135.00
Purchase #7	$228.96	11.573%	$255.4575	$255.46	$255.45	$255.50
7 purchase totals =	$1,028.28		$1,127.2574	$1,127.26	$1,127.20	$1,127.30