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	$139.89	12.646%	$157.5805	$157.58	$157.60	$157.60
Purchase #2	$115.95	12.517%	$130.4635	$130.46	$130.45	$130.50
Purchase #3	$117.54	12.253%	$131.9422	$131.94	$131.95	$131.90
Purchase #4	$126.82	5.822%	$134.2035	$134.20	$134.20	$134.20
Purchase #5	$152.32	10.855%	$168.8543	$168.85	$168.85	$168.90
Purchase #6	$17.87	13.789%	$20.3341	$20.33	$20.35	$20.30
Purchase #7	$74.40	10.805%	$82.4389	$82.44	$82.45	$82.40
7 purchase totals =	$744.79		$825.8170	$825.80	$825.85	$825.80