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	$250.95	9.169%	$273.9596	$273.96	$273.95	$274.00
Purchase #2	$178.56	5.726%	$188.7843	$188.78	$188.80	$188.80
Purchase #3	$144.39	12.158%	$161.9449	$161.94	$161.95	$161.90
Purchase #4	$87.81	13.431%	$99.6038	$99.60	$99.60	$99.60
Purchase #5	$64.31	3.424%	$66.512	$66.51	$66.50	$66.50
Purchase #6	$144.53	11.260%	$160.8041	$160.80	$160.80	$160.80
Purchase #7	$235.87	11.854%	$263.83	$263.83	$263.85	$263.80
7 purchase totals =	$1,106.42		$1,215.4387	$1,215.42	$1,215.45	$1,215.40