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	$101.50	8.258%	$109.8819	$109.88	$109.90	$109.90
Purchase #2	$230.91	13.699%	$262.5424	$262.54	$262.55	$262.50
Purchase #3	$52.99	12.273%	$59.4935	$59.49	$59.50	$59.50
Purchase #4	$94.63	8.190%	$102.3802	$102.38	$102.40	$102.40
Purchase #5	$115.60	8.222%	$125.1046	$125.10	$125.10	$125.10
Purchase #6	$233.75	3.138%	$241.0851	$241.09	$241.10	$241.10
Purchase #7	$38.67	7.583%	$41.6023	$41.60	$41.60	$41.60
7 purchase totals =	$868.05		$942.0900	$942.08	$942.15	$942.10