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	$111.53	11.437%	$124.2857	$124.29	$124.30	$124.30
Purchase #2	$54.93	11.462%	$61.2261	$61.23	$61.25	$61.20
Purchase #3	$58.57	13.694%	$66.5906	$66.59	$66.60	$66.60
Purchase #4	$142.78	8.583%	$155.0348	$155.03	$155.05	$155.00
Purchase #5	$59.54	5.288%	$62.6885	$62.69	$62.70	$62.70
Purchase #6	$227.57	12.240%	$255.4246	$255.42	$255.40	$255.40
Purchase #7	$196.77	3.192%	$203.0509	$203.05	$203.05	$203.10
7 purchase totals =	$851.69		$928.3012	$928.30	$928.35	$928.30