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	$227.41	13.705%	$258.5765	$258.58	$258.60	$258.60
Purchase #2	$79.91	8.576%	$86.7631	$86.76	$86.75	$86.80
Purchase #3	$7.55	11.467%	$8.4158	$8.42	$8.40	$8.40
Purchase #4	$242.95	5.186%	$255.5494	$255.55	$255.55	$255.50
Purchase #5	$226.51	6.448%	$241.1154	$241.12	$241.10	$241.10
Purchase #6	$124.67	12.851%	$140.6913	$140.69	$140.70	$140.70
Purchase #7	$33.25	12.426%	$37.3816	$37.38	$37.40	$37.40
7 purchase totals =	$942.25		$1,028.4931	$1,028.50	$1,028.50	$1,028.50