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	$98.66	10.662%	$109.1791	$109.18	$109.20	$109.20
Purchase #2	$208.83	5.759%	$220.8565	$220.86	$220.85	$220.90
Purchase #3	$46.69	12.519%	$52.5351	$52.54	$52.55	$52.50
Purchase #4	$132.53	7.830%	$142.9071	$142.91	$142.90	$142.90
Purchase #5	$10.86	9.153%	$11.854	$11.85	$11.85	$11.90
Purchase #6	$241.39	12.810%	$272.3121	$272.31	$272.30	$272.30
Purchase #7	$98.93	11.622%	$110.4276	$110.43	$110.45	$110.40
7 purchase totals =	$837.89		$920.0715	$920.08	$920.10	$920.10