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	$200.44	10.329%	$221.1434	$221.14	$221.15	$221.10
Purchase #2	$140.75	3.533%	$145.7227	$145.72	$145.70	$145.70
Purchase #3	$167.49	9.691%	$183.7215	$183.72	$183.70	$183.70
Purchase #4	$31.90	3.225%	$32.9288	$32.93	$32.95	$32.90
Purchase #5	$183.38	11.509%	$204.4852	$204.49	$204.50	$204.50
Purchase #6	$107.47	3.364%	$111.0853	$111.09	$111.10	$111.10
Purchase #7	$181.32	5.299%	$190.9281	$190.93	$190.95	$190.90
7 purchase totals =	$1,012.75		$1,090.0150	$1,090.02	$1,090.05	$1,089.90