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	$122.75	11.804%	$137.2394	$137.24	$137.25	$137.20
Purchase #2	$239.34	9.655%	$262.4483	$262.45	$262.45	$262.40
Purchase #3	$70.71	13.789%	$80.4602	$80.46	$80.45	$80.50
Purchase #4	$163.41	9.855%	$179.5141	$179.51	$179.50	$179.50
Purchase #5	$80.68	12.608%	$90.8521	$90.85	$90.85	$90.90
Purchase #6	$6.94	11.215%	$7.7183	$7.72	$7.70	$7.70
Purchase #7	$46.96	7.856%	$50.6492	$50.65	$50.65	$50.60
7 purchase totals =	$730.79		$808.8816	$808.88	$808.85	$808.80