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	$56.58	8.737%	$61.5234	$61.52	$61.50	$61.50
Purchase #2	$135.47	6.743%	$144.6047	$144.60	$144.60	$144.60
Purchase #3	$244.91	7.183%	$262.5019	$262.50	$262.50	$262.50
Purchase #4	$180.84	9.771%	$198.5099	$198.51	$198.50	$198.50
Purchase #5	$63.46	6.177%	$67.3799	$67.38	$67.40	$67.40
Purchase #6	$30.91	12.510%	$34.7768	$34.78	$34.80	$34.80
Purchase #7	$142.89	3.840%	$148.377	$148.38	$148.40	$148.40
7 purchase totals =	$855.06		$917.6736	$917.67	$917.70	$917.70