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	$51.68	8.382%	$56.0118	$56.01	$56.00	$56.00
Purchase #2	$19.60	7.304%	$21.0316	$21.03	$21.05	$21.00
Purchase #3	$230.61	11.743%	$257.6905	$257.69	$257.70	$257.70
Purchase #4	$161.40	11.233%	$179.5301	$179.53	$179.55	$179.50
Purchase #5	$50.57	13.126%	$57.2078	$57.21	$57.20	$57.20
Purchase #6	$81.93	12.664%	$92.3056	$92.31	$92.30	$92.30
Purchase #7	$72.80	13.342%	$82.513	$82.51	$82.50	$82.50
7 purchase totals =	$668.59		$746.2904	$746.29	$746.30	$746.20