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	$16.32	10.139%	$17.9747	$17.97	$17.95	$18.00
Purchase #2	$241.95	4.759%	$253.4644	$253.46	$253.45	$253.50
Purchase #3	$208.54	9.783%	$228.9415	$228.94	$228.95	$228.90
Purchase #4	$174.85	12.215%	$196.2079	$196.21	$196.20	$196.20
Purchase #5	$38.40	12.454%	$43.1823	$43.18	$43.20	$43.20
Purchase #6	$209.83	3.181%	$216.5047	$216.50	$216.50	$216.50
Purchase #7	$60.33	3.632%	$62.5212	$62.52	$62.50	$62.50
7 purchase totals =	$950.22		$1,018.7967	$1,018.78	$1,018.75	$1,018.80