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	$113.29	11.295%	$126.0861	$126.09	$126.10	$126.10
Purchase #2	$130.77	6.599%	$139.3995	$139.40	$139.40	$139.40
Purchase #3	$105.61	12.852%	$119.183	$119.18	$119.20	$119.20
Purchase #4	$143.96	11.569%	$160.6147	$160.61	$160.60	$160.60
Purchase #5	$155.76	4.349%	$162.534	$162.53	$162.55	$162.50
Purchase #6	$166.63	9.382%	$182.2632	$182.26	$182.25	$182.30
Purchase #7	$83.80	5.869%	$88.7182	$88.72	$88.70	$88.70
7 purchase totals =	$899.82		$978.7987	$978.79	$978.80	$978.80