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	$34.82	7.720%	$37.5081	$37.51	$37.50	$37.50
Purchase #2	$49.63	5.236%	$52.2286	$52.23	$52.25	$52.20
Purchase #3	$115.35	11.724%	$128.8736	$128.87	$128.85	$128.90
Purchase #4	$27.27	9.407%	$29.8353	$29.84	$29.85	$29.80
Purchase #5	$249.81	5.326%	$263.1149	$263.11	$263.10	$263.10
Purchase #6	$158.25	13.758%	$180.022	$180.02	$180.00	$180.00
Purchase #7	$135.83	6.693%	$144.9211	$144.92	$144.90	$144.90
7 purchase totals =	$770.96		$836.5036	$836.50	$836.45	$836.40