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	$131.25	6.270%	$139.4794	$139.48	$139.50	$139.50
Purchase #2	$198.51	9.166%	$216.7054	$216.71	$216.70	$216.70
Purchase #3	$176.49	13.606%	$200.5032	$200.50	$200.50	$200.50
Purchase #4	$249.29	13.203%	$282.2038	$282.20	$282.20	$282.20
Purchase #5	$128.46	12.172%	$144.0962	$144.10	$144.10	$144.10
Purchase #6	$55.48	13.159%	$62.7806	$62.78	$62.80	$62.80
Purchase #7	$22.95	9.470%	$25.1234	$25.12	$25.10	$25.10
7 purchase totals =	$962.43		$1,070.8920	$1,070.89	$1,070.90	$1,070.90