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	$86.40	4.245%	$90.0677	$90.07	$90.05	$90.10
Purchase #2	$52.64	3.541%	$54.504	$54.50	$54.50	$54.50
Purchase #3	$133.81	4.466%	$139.786	$139.79	$139.80	$139.80
Purchase #4	$121.71	9.375%	$133.1203	$133.12	$133.10	$133.10
Purchase #5	$225.25	7.558%	$242.2744	$242.27	$242.25	$242.30
Purchase #6	$178.75	3.267%	$184.5898	$184.59	$184.60	$184.60
Purchase #7	$106.72	5.507%	$112.5971	$112.60	$112.60	$112.60
7 purchase totals =	$905.28		$956.9393	$956.94	$956.90	$957.00