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	$234.38	13.481%	$265.9768	$265.98	$266.00	$266.00
Purchase #2	$68.80	4.189%	$71.682	$71.68	$71.70	$71.70
Purchase #3	$120.38	5.142%	$126.5699	$126.57	$126.55	$126.60
Purchase #4	$52.36	6.540%	$55.7843	$55.78	$55.80	$55.80
Purchase #5	$178.55	5.526%	$188.4167	$188.42	$188.40	$188.40
Purchase #6	$35.59	4.723%	$37.2709	$37.27	$37.25	$37.30
Purchase #7	$74.80	3.193%	$77.1884	$77.19	$77.20	$77.20
7 purchase totals =	$764.86		$822.8890	$822.89	$822.90	$823.00