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	$153.81	6.599%	$163.9599	$163.96	$163.95	$164.00
Purchase #2	$123.97	7.646%	$133.4487	$133.45	$133.45	$133.40
Purchase #3	$51.50	9.830%	$56.5625	$56.56	$56.55	$56.60
Purchase #4	$32.75	13.636%	$37.2158	$37.22	$37.20	$37.20
Purchase #5	$77.32	12.323%	$86.8481	$86.85	$86.85	$86.80
Purchase #6	$193.71	3.478%	$200.4472	$200.45	$200.45	$200.40
Purchase #7	$126.31	12.276%	$141.8158	$141.82	$141.80	$141.80
7 purchase totals =	$759.37		$820.2980	$820.31	$820.25	$820.20