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	$192.69	12.680%	$217.1231	$217.12	$217.10	$217.10
Purchase #2	$74.57	4.516%	$77.9376	$77.94	$77.95	$77.90
Purchase #3	$106.43	4.725%	$111.4588	$111.46	$111.45	$111.50
Purchase #4	$139.42	10.691%	$154.3254	$154.33	$154.35	$154.30
Purchase #5	$77.98	9.467%	$85.3624	$85.36	$85.35	$85.40
Purchase #6	$96.37	7.864%	$103.9485	$103.95	$103.95	$103.90
Purchase #7	$135.53	4.647%	$141.8281	$141.83	$141.85	$141.80
7 purchase totals =	$822.99		$891.9839	$891.99	$892.00	$891.90