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	$73.70	6.635%	$78.59	$78.59	$78.60	$78.60
Purchase #2	$36.31	13.493%	$41.2093	$41.21	$41.20	$41.20
Purchase #3	$113.81	3.623%	$117.9333	$117.93	$117.95	$117.90
Purchase #4	$205.75	9.450%	$225.1934	$225.19	$225.20	$225.20
Purchase #5	$188.36	4.537%	$196.9059	$196.91	$196.90	$196.90
Purchase #6	$71.66	10.366%	$79.0883	$79.09	$79.10	$79.10
Purchase #7	$112.78	12.472%	$126.8459	$126.85	$126.85	$126.80
7 purchase totals =	$802.37		$865.7661	$865.77	$865.80	$865.70