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	$211.94	12.420%	$238.2629	$238.26	$238.25	$238.30
Purchase #2	$161.56	10.539%	$178.5868	$178.59	$178.60	$178.60
Purchase #3	$131.27	10.336%	$144.8381	$144.84	$144.85	$144.80
Purchase #4	$40.59	3.825%	$42.1426	$42.14	$42.15	$42.10
Purchase #5	$132.86	10.297%	$146.5406	$146.54	$146.55	$146.50
Purchase #6	$146.76	11.497%	$163.633	$163.63	$163.65	$163.60
Purchase #7	$204.73	6.401%	$217.8348	$217.83	$217.85	$217.80
7 purchase totals =	$1,029.71		$1,131.8388	$1,131.83	$1,131.90	$1,131.70