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	$132.50	10.801%	$146.8113	$146.81	$146.80	$146.80
Purchase #2	$42.85	12.785%	$48.3284	$48.33	$48.35	$48.30
Purchase #3	$246.90	13.208%	$279.5106	$279.51	$279.50	$279.50
Purchase #4	$72.53	10.180%	$79.9136	$79.91	$79.90	$79.90
Purchase #5	$122.66	3.684%	$127.1788	$127.18	$127.20	$127.20
Purchase #6	$164.75	7.155%	$176.5379	$176.54	$176.55	$176.50
Purchase #7	$10.91	4.861%	$11.4403	$11.44	$11.45	$11.40
7 purchase totals =	$793.10		$869.7209	$869.72	$869.75	$869.60