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	$139.46	3.527%	$144.3788	$144.38	$144.40	$144.40
Purchase #2	$178.32	6.355%	$189.6522	$189.65	$189.65	$189.70
Purchase #3	$157.50	7.135%	$168.7376	$168.74	$168.75	$168.70
Purchase #4	$134.78	4.436%	$140.7588	$140.76	$140.75	$140.80
Purchase #5	$87.60	3.370%	$90.5521	$90.55	$90.55	$90.60
Purchase #6	$153.52	7.142%	$164.4844	$164.48	$164.50	$164.50
Purchase #7	$225.74	10.786%	$250.0883	$250.09	$250.10	$250.10
7 purchase totals =	$1,076.92		$1,148.6522	$1,148.65	$1,148.70	$1,148.80