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	$98.81	12.579%	$111.2393	$111.24	$111.25	$111.20
Purchase #2	$37.61	12.354%	$42.2563	$42.26	$42.25	$42.30
Purchase #3	$168.87	10.480%	$186.5676	$186.57	$186.55	$186.60
Purchase #4	$150.32	5.466%	$158.5365	$158.54	$158.55	$158.50
Purchase #5	$175.50	4.714%	$183.7731	$183.77	$183.75	$183.80
Purchase #6	$218.55	10.396%	$241.2705	$241.27	$241.25	$241.30
Purchase #7	$102.66	5.224%	$108.023	$108.02	$108.00	$108.00
7 purchase totals =	$952.32		$1,031.6663	$1,031.67	$1,031.60	$1,031.70