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	$139.59	6.190%	$148.2306	$148.23	$148.25	$148.20
Purchase #2	$241.93	8.514%	$262.5279	$262.53	$262.55	$262.50
Purchase #3	$198.75	4.793%	$208.2761	$208.28	$208.30	$208.30
Purchase #4	$155.29	9.719%	$170.3826	$170.38	$170.40	$170.40
Purchase #5	$147.91	3.239%	$152.7008	$152.70	$152.70	$152.70
Purchase #6	$54.36	9.451%	$59.4976	$59.50	$59.50	$59.50
Purchase #7	$132.63	3.701%	$137.5386	$137.54	$137.55	$137.50
7 purchase totals =	$1,070.46		$1,139.1542	$1,139.16	$1,139.25	$1,139.10