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	$44.37	12.451%	$49.8945	$49.89	$49.90	$49.90
Purchase #2	$125.65	11.776%	$140.4465	$140.45	$140.45	$140.40
Purchase #3	$248.52	4.319%	$259.2536	$259.25	$259.25	$259.30
Purchase #4	$158.51	4.451%	$165.5653	$165.57	$165.55	$165.60
Purchase #5	$210.88	10.665%	$233.3704	$233.37	$233.35	$233.40
Purchase #6	$35.66	12.243%	$40.0259	$40.03	$40.05	$40.00
Purchase #7	$149.55	10.605%	$165.4098	$165.41	$165.40	$165.40
7 purchase totals =	$973.14		$1,053.9660	$1,053.97	$1,053.95	$1,054.00