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	$120.50	11.236%	$134.0394	$134.04	$134.05	$134.00
Purchase #2	$36.45	6.627%	$38.8655	$38.87	$38.85	$38.90
Purchase #3	$116.64	5.787%	$123.39	$123.39	$123.40	$123.40
Purchase #4	$55.51	7.302%	$59.5633	$59.56	$59.55	$59.60
Purchase #5	$42.92	4.227%	$44.7342	$44.73	$44.75	$44.70
Purchase #6	$130.30	10.207%	$143.5997	$143.60	$143.60	$143.60
Purchase #7	$186.52	7.238%	$200.0203	$200.02	$200.00	$200.00
7 purchase totals =	$688.84		$744.2124	$744.21	$744.20	$744.20