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	$150.49	3.206%	$155.3147	$155.31	$155.30	$155.30
Purchase #2	$226.91	12.756%	$255.8546	$255.85	$255.85	$255.90
Purchase #3	$143.68	8.630%	$156.0796	$156.08	$156.10	$156.10
Purchase #4	$213.51	7.874%	$230.3218	$230.32	$230.30	$230.30
Purchase #5	$77.97	10.872%	$86.4469	$86.45	$86.45	$86.40
Purchase #6	$193.45	13.398%	$219.3684	$219.37	$219.35	$219.40
Purchase #7	$111.32	7.118%	$119.2438	$119.24	$119.25	$119.20
7 purchase totals =	$1,117.33		$1,222.6298	$1,222.62	$1,222.60	$1,222.60