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	$247.98	8.718%	$269.5989	$269.60	$269.60	$269.60
Purchase #2	$238.42	9.705%	$261.5587	$261.56	$261.55	$261.60
Purchase #3	$86.58	3.382%	$89.5081	$89.51	$89.50	$89.50
Purchase #4	$84.90	6.550%	$90.461	$90.46	$90.45	$90.50
Purchase #5	$226.90	12.832%	$256.0158	$256.02	$256.00	$256.00
Purchase #6	$25.63	3.202%	$26.4507	$26.45	$26.45	$26.50
Purchase #7	$47.85	4.667%	$50.0832	$50.08	$50.10	$50.10
7 purchase totals =	$958.26		$1,043.6764	$1,043.68	$1,043.65	$1,043.80