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	$170.73	12.681%	$192.3803	$192.38	$192.40	$192.40
Purchase #2	$91.43	3.586%	$94.7087	$94.71	$94.70	$94.70
Purchase #3	$98.41	13.321%	$111.5192	$111.52	$111.50	$111.50
Purchase #4	$144.96	3.833%	$150.5163	$150.52	$150.50	$150.50
Purchase #5	$203.73	13.313%	$230.8526	$230.85	$230.85	$230.90
Purchase #6	$102.71	8.592%	$111.5348	$111.53	$111.55	$111.50
Purchase #7	$44.56	11.672%	$49.761	$49.76	$49.75	$49.80
7 purchase totals =	$856.53		$941.2729	$941.27	$941.25	$941.30