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	$246.75	13.628%	$280.3771	$280.38	$280.40	$280.40
Purchase #2	$121.71	9.517%	$133.2931	$133.29	$133.30	$133.30
Purchase #3	$30.73	6.102%	$32.6051	$32.61	$32.60	$32.60
Purchase #4	$51.83	4.164%	$53.9882	$53.99	$54.00	$54.00
Purchase #5	$241.43	3.329%	$249.4672	$249.47	$249.45	$249.50
Purchase #6	$113.59	13.247%	$128.6373	$128.64	$128.65	$128.60
Purchase #7	$159.74	3.262%	$164.9507	$164.95	$164.95	$165.00
7 purchase totals =	$965.78		$1,043.3187	$1,043.33	$1,043.35	$1,043.40