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	$154.81	6.287%	$164.5429	$164.54	$164.55	$164.50
Purchase #2	$170.94	8.810%	$185.9998	$186.00	$186.00	$186.00
Purchase #3	$80.69	10.832%	$89.4303	$89.43	$89.45	$89.40
Purchase #4	$149.63	12.670%	$168.5881	$168.59	$168.60	$168.60
Purchase #5	$117.83	4.565%	$123.2089	$123.21	$123.20	$123.20
Purchase #6	$157.96	11.827%	$176.6419	$176.64	$176.65	$176.60
Purchase #7	$52.41	10.245%	$57.7794	$57.78	$57.80	$57.80
7 purchase totals =	$884.27		$966.1913	$966.19	$966.25	$966.10