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	$53.98	10.248%	$59.5119	$59.51	$59.50	$59.50
Purchase #2	$46.88	10.789%	$51.9379	$51.94	$51.95	$51.90
Purchase #3	$21.35	8.724%	$23.2126	$23.21	$23.20	$23.20
Purchase #4	$109.87	12.708%	$123.8323	$123.83	$123.85	$123.80
Purchase #5	$55.50	4.363%	$57.9215	$57.92	$57.90	$57.90
Purchase #6	$188.76	4.562%	$197.3712	$197.37	$197.35	$197.40
Purchase #7	$64.29	5.568%	$67.8697	$67.87	$67.85	$67.90
7 purchase totals =	$540.63		$581.6571	$581.65	$581.60	$581.60