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	$123.36	12.389%	$138.6431	$138.64	$138.65	$138.60
Purchase #2	$146.25	8.580%	$158.7983	$158.80	$158.80	$158.80
Purchase #3	$114.54	11.657%	$127.8919	$127.89	$127.90	$127.90
Purchase #4	$19.87	10.320%	$21.9206	$21.92	$21.90	$21.90
Purchase #5	$18.60	7.280%	$19.9541	$19.95	$19.95	$20.00
Purchase #6	$239.29	6.535%	$254.9276	$254.93	$254.95	$254.90
Purchase #7	$90.33	8.699%	$98.1878	$98.19	$98.20	$98.20
7 purchase totals =	$752.24		$820.3234	$820.32	$820.35	$820.30