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	$51.89	12.712%	$58.4863	$58.49	$58.50	$58.50
Purchase #2	$25.27	8.708%	$27.4705	$27.47	$27.45	$27.50
Purchase #3	$230.31	12.393%	$258.8523	$258.85	$258.85	$258.90
Purchase #4	$200.28	4.276%	$208.844	$208.84	$208.85	$208.80
Purchase #5	$179.70	5.379%	$189.3661	$189.37	$189.35	$189.40
Purchase #6	$106.28	10.463%	$117.4001	$117.40	$117.40	$117.40
Purchase #7	$112.61	9.640%	$123.4656	$123.47	$123.45	$123.50
7 purchase totals =	$906.34		$983.8849	$983.89	$983.85	$984.00