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	$146.97	8.761%	$159.846	$159.85	$159.85	$159.80
Purchase #2	$128.80	13.838%	$146.6233	$146.62	$146.60	$146.60
Purchase #3	$137.74	13.588%	$156.4561	$156.46	$156.45	$156.50
Purchase #4	$73.28	9.127%	$79.9683	$79.97	$79.95	$80.00
Purchase #5	$128.50	8.362%	$139.2452	$139.25	$139.25	$139.20
Purchase #6	$75.50	4.436%	$78.8492	$78.85	$78.85	$78.80
Purchase #7	$128.48	10.368%	$141.8008	$141.80	$141.80	$141.80
7 purchase totals =	$819.27		$902.7889	$902.80	$902.75	$902.70