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	$148.90	13.799%	$169.4467	$169.45	$169.45	$169.40
Purchase #2	$190.80	9.258%	$208.4643	$208.46	$208.45	$208.50
Purchase #3	$156.51	12.819%	$176.573	$176.57	$176.55	$176.60
Purchase #4	$31.49	4.622%	$32.9455	$32.95	$32.95	$32.90
Purchase #5	$55.39	13.177%	$62.6887	$62.69	$62.70	$62.70
Purchase #6	$152.35	4.278%	$158.8675	$158.87	$158.85	$158.90
Purchase #7	$65.80	7.224%	$70.5534	$70.55	$70.55	$70.60
7 purchase totals =	$801.24		$879.5391	$879.54	$879.50	$879.60