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	$15.30	3.220%	$15.7927	$15.79	$15.80	$15.80
Purchase #2	$11.71	4.570%	$12.2451	$12.25	$12.25	$12.20
Purchase #3	$156.64	10.271%	$172.7285	$172.73	$172.75	$172.70
Purchase #4	$38.59	13.218%	$43.6908	$43.69	$43.70	$43.70
Purchase #5	$132.66	12.224%	$148.8764	$148.88	$148.90	$148.90
Purchase #6	$54.67	5.426%	$57.6364	$57.64	$57.65	$57.60
Purchase #7	$84.47	7.508%	$90.812	$90.81	$90.80	$90.80
7 purchase totals =	$494.04		$541.7819	$541.79	$541.85	$541.70