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	$105.94	5.277%	$111.5305	$111.53	$111.55	$111.50
Purchase #2	$89.54	11.713%	$100.0278	$100.03	$100.05	$100.00
Purchase #3	$164.82	12.487%	$185.4011	$185.40	$185.40	$185.40
Purchase #4	$177.92	7.166%	$190.6697	$190.67	$190.65	$190.70
Purchase #5	$237.66	3.322%	$245.5551	$245.56	$245.55	$245.60
Purchase #6	$133.48	10.836%	$147.9439	$147.94	$147.95	$147.90
Purchase #7	$48.56	3.119%	$50.0746	$50.07	$50.05	$50.10
7 purchase totals =	$957.92		$1,031.2027	$1,031.20	$1,031.20	$1,031.20