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	$17.98	11.705%	$20.0846	$20.08	$20.10	$20.10
Purchase #2	$128.48	12.864%	$145.0077	$145.01	$145.00	$145.00
Purchase #3	$186.68	3.111%	$192.4876	$192.49	$192.50	$192.50
Purchase #4	$103.30	12.724%	$116.4439	$116.44	$116.45	$116.40
Purchase #5	$188.97	11.467%	$210.6392	$210.64	$210.65	$210.60
Purchase #6	$24.90	13.608%	$28.2884	$28.29	$28.30	$28.30
Purchase #7	$179.94	9.252%	$196.588	$196.59	$196.60	$196.60
7 purchase totals =	$830.25		$909.5394	$909.54	$909.60	$909.50