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	$159.52	13.836%	$181.5912	$181.59	$181.60	$181.60
Purchase #2	$86.47	3.421%	$89.4281	$89.43	$89.45	$89.40
Purchase #3	$34.75	7.308%	$37.2895	$37.29	$37.30	$37.30
Purchase #4	$105.52	13.663%	$119.9372	$119.94	$119.95	$119.90
Purchase #5	$87.38	6.869%	$93.3821	$93.38	$93.40	$93.40
Purchase #6	$20.65	11.505%	$23.0258	$23.03	$23.05	$23.00
Purchase #7	$32.86	6.338%	$34.9427	$34.94	$34.95	$34.90
7 purchase totals =	$527.15		$579.5966	$579.60	$579.70	$579.50