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	$229.41	5.322%	$241.6192	$241.62	$241.60	$241.60
Purchase #2	$164.85	5.106%	$173.2672	$173.27	$173.25	$173.30
Purchase #3	$86.81	6.437%	$92.398	$92.40	$92.40	$92.40
Purchase #4	$226.92	11.839%	$253.7851	$253.79	$253.80	$253.80
Purchase #5	$80.92	11.760%	$90.4362	$90.44	$90.45	$90.40
Purchase #6	$50.85	4.149%	$52.9598	$52.96	$52.95	$53.00
Purchase #7	$75.95	3.438%	$78.5612	$78.56	$78.55	$78.60
7 purchase totals =	$915.71		$983.0267	$983.04	$983.00	$983.10