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	$9.72	7.421%	$10.4413	$10.44	$10.45	$10.40
Purchase #2	$228.36	13.763%	$259.7892	$259.79	$259.80	$259.80
Purchase #3	$132.97	13.786%	$151.3012	$151.30	$151.30	$151.30
Purchase #4	$56.59	5.734%	$59.8349	$59.83	$59.85	$59.80
Purchase #5	$25.90	13.194%	$29.3172	$29.32	$29.30	$29.30
Purchase #6	$186.94	10.238%	$206.0789	$206.08	$206.10	$206.10
Purchase #7	$228.36	12.340%	$256.5396	$256.54	$256.55	$256.50
7 purchase totals =	$868.84		$973.3023	$973.30	$973.35	$973.20