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	$138.32	4.338%	$144.3203	$144.32	$144.30	$144.30
Purchase #2	$74.57	3.857%	$77.4462	$77.45	$77.45	$77.40
Purchase #3	$200.74	10.757%	$222.3336	$222.33	$222.35	$222.30
Purchase #4	$167.57	7.130%	$179.5177	$179.52	$179.50	$179.50
Purchase #5	$205.46	10.772%	$227.5922	$227.59	$227.60	$227.60
Purchase #6	$233.39	13.317%	$264.4705	$264.47	$264.45	$264.50
Purchase #7	$184.74	8.409%	$200.2748	$200.27	$200.25	$200.30
7 purchase totals =	$1,204.79		$1,315.9553	$1,315.95	$1,315.90	$1,315.90