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	$82.58	13.230%	$93.5053	$93.51	$93.50	$93.50
Purchase #2	$111.86	6.692%	$119.3457	$119.35	$119.35	$119.30
Purchase #3	$137.71	13.465%	$156.2527	$156.25	$156.25	$156.30
Purchase #4	$69.82	11.713%	$77.998	$78.00	$78.00	$78.00
Purchase #5	$220.92	4.246%	$230.3003	$230.30	$230.30	$230.30
Purchase #6	$30.70	10.375%	$33.8851	$33.89	$33.90	$33.90
Purchase #7	$103.30	8.767%	$112.3563	$112.36	$112.35	$112.40
7 purchase totals =	$756.89		$823.6434	$823.66	$823.65	$823.70