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	$155.97	6.705%	$166.4278	$166.43	$166.45	$166.40
Purchase #2	$248.54	10.628%	$274.9548	$274.95	$274.95	$275.00
Purchase #3	$196.56	4.710%	$205.818	$205.82	$205.80	$205.80
Purchase #4	$33.85	13.209%	$38.3212	$38.32	$38.30	$38.30
Purchase #5	$190.90	10.356%	$210.6696	$210.67	$210.65	$210.70
Purchase #6	$32.65	4.785%	$34.2123	$34.21	$34.20	$34.20
Purchase #7	$137.33	9.494%	$150.3681	$150.37	$150.35	$150.40
7 purchase totals =	$995.80		$1,080.7718	$1,080.77	$1,080.70	$1,080.80