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	$159.63	5.522%	$168.4448	$168.44	$168.45	$168.40
Purchase #2	$124.64	10.173%	$137.3196	$137.32	$137.30	$137.30
Purchase #3	$182.36	4.488%	$190.5443	$190.54	$190.55	$190.50
Purchase #4	$209.91	7.208%	$225.0403	$225.04	$225.05	$225.00
Purchase #5	$243.86	5.749%	$257.8795	$257.88	$257.90	$257.90
Purchase #6	$117.52	12.672%	$132.4121	$132.41	$132.40	$132.40
Purchase #7	$179.53	3.350%	$185.5443	$185.54	$185.55	$185.50
7 purchase totals =	$1,217.45		$1,297.1849	$1,297.17	$1,297.20	$1,297.00