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	$173.53	13.289%	$196.5904	$196.59	$196.60	$196.60
Purchase #2	$34.74	13.353%	$39.3788	$39.38	$39.40	$39.40
Purchase #3	$56.62	12.260%	$63.5616	$63.56	$63.55	$63.60
Purchase #4	$42.54	10.168%	$46.8655	$46.87	$46.85	$46.90
Purchase #5	$240.51	12.661%	$270.961	$270.96	$270.95	$271.00
Purchase #6	$9.53	13.680%	$10.8337	$10.83	$10.85	$10.80
Purchase #7	$67.46	6.193%	$71.6378	$71.64	$71.65	$71.60
7 purchase totals =	$624.93		$699.8288	$699.83	$699.85	$699.90