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	$42.79	12.637%	$48.1974	$48.20	$48.20	$48.20
Purchase #2	$146.79	9.362%	$160.5325	$160.53	$160.55	$160.50
Purchase #3	$238.64	3.208%	$246.2956	$246.30	$246.30	$246.30
Purchase #4	$132.88	7.264%	$142.5324	$142.53	$142.55	$142.50
Purchase #5	$147.40	4.833%	$154.5238	$154.52	$154.50	$154.50
Purchase #6	$40.47	4.576%	$42.3219	$42.32	$42.30	$42.30
Purchase #7	$226.40	3.313%	$233.9006	$233.90	$233.90	$233.90
7 purchase totals =	$975.37		$1,028.3042	$1,028.30	$1,028.30	$1,028.20