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	$80.54	12.308%	$90.4529	$90.45	$90.45	$90.50
Purchase #2	$38.68	9.753%	$42.4525	$42.45	$42.45	$42.50
Purchase #3	$241.38	7.510%	$259.5076	$259.51	$259.50	$259.50
Purchase #4	$48.58	3.157%	$50.1137	$50.11	$50.10	$50.10
Purchase #5	$98.81	5.271%	$104.0183	$104.02	$104.00	$104.00
Purchase #6	$150.46	9.431%	$164.6499	$164.65	$164.65	$164.60
Purchase #7	$155.93	13.143%	$176.4239	$176.42	$176.40	$176.40
7 purchase totals =	$814.38		$887.6188	$887.61	$887.55	$887.60