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	$249.74	3.865%	$259.3925	$259.39	$259.40	$259.40
Purchase #2	$175.37	12.275%	$196.8967	$196.90	$196.90	$196.90
Purchase #3	$215.93	10.238%	$238.0369	$238.04	$238.05	$238.00
Purchase #4	$34.40	11.186%	$38.248	$38.25	$38.25	$38.20
Purchase #5	$198.26	10.724%	$219.5214	$219.52	$219.50	$219.50
Purchase #6	$248.83	10.380%	$274.6586	$274.66	$274.65	$274.70
Purchase #7	$152.86	3.518%	$158.2376	$158.24	$158.25	$158.20
7 purchase totals =	$1,275.39		$1,384.9917	$1,385.00	$1,385.00	$1,384.90