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	$37.66	7.509%	$40.4879	$40.49	$40.50	$40.50
Purchase #2	$133.35	12.823%	$150.4495	$150.45	$150.45	$150.40
Purchase #3	$35.96	13.864%	$40.9455	$40.95	$40.95	$40.90
Purchase #4	$105.77	6.750%	$112.9095	$112.91	$112.90	$112.90
Purchase #5	$202.48	5.557%	$213.7318	$213.73	$213.75	$213.70
Purchase #6	$229.42	11.374%	$255.5142	$255.51	$255.50	$255.50
Purchase #7	$250.62	3.136%	$258.4794	$258.48	$258.50	$258.50
7 purchase totals =	$995.26		$1,072.5178	$1,072.52	$1,072.55	$1,072.40