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	$136.25	9.277%	$148.8899	$148.89	$148.90	$148.90
Purchase #2	$102.89	4.513%	$107.5334	$107.53	$107.55	$107.50
Purchase #3	$39.64	11.837%	$44.3322	$44.33	$44.35	$44.30
Purchase #4	$129.28	11.293%	$143.8796	$143.88	$143.90	$143.90
Purchase #5	$73.63	13.772%	$83.7703	$83.77	$83.75	$83.80
Purchase #6	$127.67	7.764%	$137.5823	$137.58	$137.60	$137.60
Purchase #7	$188.47	13.813%	$214.5034	$214.50	$214.50	$214.50
7 purchase totals =	$797.83		$880.4911	$880.48	$880.55	$880.50