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	$151.45	9.223%	$165.4182	$165.42	$165.40	$165.40
Purchase #2	$158.77	3.642%	$164.5524	$164.55	$164.55	$164.60
Purchase #3	$150.27	12.689%	$169.3378	$169.34	$169.35	$169.30
Purchase #4	$224.26	11.737%	$250.5814	$250.58	$250.60	$250.60
Purchase #5	$20.60	11.833%	$23.0376	$23.04	$23.05	$23.00
Purchase #6	$58.62	13.623%	$66.6058	$66.61	$66.60	$66.60
Purchase #7	$93.31	7.176%	$100.0059	$100.01	$100.00	$100.00
7 purchase totals =	$857.28		$939.5391	$939.55	$939.55	$939.50