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	$129.87	11.767%	$145.1518	$145.15	$145.15	$145.20
Purchase #2	$37.84	13.565%	$42.973	$42.97	$42.95	$43.00
Purchase #3	$82.90	9.523%	$90.7946	$90.79	$90.80	$90.80
Purchase #4	$234.51	13.284%	$265.6623	$265.66	$265.65	$265.70
Purchase #5	$138.61	4.300%	$144.5702	$144.57	$144.55	$144.60
Purchase #6	$131.80	6.344%	$140.1614	$140.16	$140.15	$140.20
Purchase #7	$144.95	10.704%	$160.4654	$160.47	$160.45	$160.50
7 purchase totals =	$900.48		$989.7787	$989.77	$989.70	$990.00