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	$56.79	12.556%	$63.9206	$63.92	$63.90	$63.90
Purchase #2	$178.82	3.189%	$184.5226	$184.52	$184.50	$184.50
Purchase #3	$35.52	5.802%	$37.5809	$37.58	$37.60	$37.60
Purchase #4	$37.52	7.653%	$40.3914	$40.39	$40.40	$40.40
Purchase #5	$142.60	8.220%	$154.3217	$154.32	$154.30	$154.30
Purchase #6	$172.68	8.427%	$187.2317	$187.23	$187.25	$187.20
Purchase #7	$28.79	9.784%	$31.6068	$31.61	$31.60	$31.60
7 purchase totals =	$652.72		$699.5757	$699.57	$699.55	$699.50