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	$37.63	8.795%	$40.9396	$40.94	$40.95	$40.90
Purchase #2	$131.74	4.800%	$138.0635	$138.06	$138.05	$138.10
Purchase #3	$116.65	9.149%	$127.3223	$127.32	$127.30	$127.30
Purchase #4	$82.98	8.443%	$89.986	$89.99	$90.00	$90.00
Purchase #5	$13.53	11.513%	$15.0877	$15.09	$15.10	$15.10
Purchase #6	$50.28	3.571%	$52.0755	$52.08	$52.10	$52.10
Purchase #7	$190.75	6.770%	$203.6638	$203.66	$203.65	$203.70
7 purchase totals =	$623.56		$667.1384	$667.14	$667.15	$667.20