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	$234.29	10.289%	$258.3961	$258.40	$258.40	$258.40
Purchase #2	$168.87	12.762%	$190.4212	$190.42	$190.40	$190.40
Purchase #3	$167.84	8.713%	$182.4639	$182.46	$182.45	$182.50
Purchase #4	$33.89	13.285%	$38.3923	$38.39	$38.40	$38.40
Purchase #5	$183.29	4.366%	$191.2924	$191.29	$191.30	$191.30
Purchase #6	$78.70	10.861%	$87.2476	$87.25	$87.25	$87.20
Purchase #7	$162.68	10.480%	$179.7289	$179.73	$179.75	$179.70
7 purchase totals =	$1,029.56		$1,127.9424	$1,127.94	$1,127.95	$1,127.90