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	$205.33	4.490%	$214.5493	$214.55	$214.55	$214.50
Purchase #2	$58.71	6.675%	$62.6289	$62.63	$62.65	$62.60
Purchase #3	$98.27	6.814%	$104.9661	$104.97	$104.95	$105.00
Purchase #4	$182.65	5.374%	$192.4656	$192.47	$192.45	$192.50
Purchase #5	$82.87	7.712%	$89.2609	$89.26	$89.25	$89.30
Purchase #6	$47.47	3.123%	$48.9525	$48.95	$48.95	$49.00
Purchase #7	$100.75	6.803%	$107.604	$107.60	$107.60	$107.60
7 purchase totals =	$776.05		$820.4273	$820.43	$820.40	$820.50