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	$132.45	3.869%	$137.5745	$137.57	$137.55	$137.60
Purchase #2	$59.40	13.599%	$67.4778	$67.48	$67.50	$67.50
Purchase #3	$234.38	7.137%	$251.1077	$251.11	$251.10	$251.10
Purchase #4	$126.39	10.654%	$139.8556	$139.86	$139.85	$139.90
Purchase #5	$119.53	8.426%	$129.6016	$129.60	$129.60	$129.60
Purchase #6	$203.29	9.538%	$222.6798	$222.68	$222.70	$222.70
Purchase #7	$153.46	8.447%	$166.4228	$166.42	$166.40	$166.40
7 purchase totals =	$1,028.90		$1,114.7198	$1,114.72	$1,114.70	$1,114.80