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	$10.83	11.719%	$12.0992	$12.10	$12.10	$12.10
Purchase #2	$137.95	11.510%	$153.828	$153.83	$153.85	$153.80
Purchase #3	$240.39	6.139%	$255.1475	$255.15	$255.15	$255.10
Purchase #4	$105.94	3.276%	$109.4106	$109.41	$109.40	$109.40
Purchase #5	$12.96	8.425%	$14.0519	$14.05	$14.05	$14.10
Purchase #6	$201.49	12.460%	$226.5957	$226.60	$226.60	$226.60
Purchase #7	$189.31	3.618%	$196.1592	$196.16	$196.15	$196.20
7 purchase totals =	$898.87		$967.2921	$967.30	$967.30	$967.30