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	$159.34	13.745%	$181.2413	$181.24	$181.25	$181.20
Purchase #2	$156.71	12.693%	$176.6012	$176.60	$176.60	$176.60
Purchase #3	$197.72	6.640%	$210.8486	$210.85	$210.85	$210.80
Purchase #4	$143.67	11.598%	$160.3328	$160.33	$160.35	$160.30
Purchase #5	$195.69	10.307%	$215.8598	$215.86	$215.85	$215.90
Purchase #6	$87.75	13.392%	$99.5015	$99.50	$99.50	$99.50
Purchase #7	$24.45	12.699%	$27.5549	$27.55	$27.55	$27.60
7 purchase totals =	$965.33		$1,071.9401	$1,071.93	$1,071.95	$1,071.90