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	$52.40	13.191%	$59.3121	$59.31	$59.30	$59.30
Purchase #2	$47.84	13.824%	$54.4534	$54.45	$54.45	$54.50
Purchase #3	$225.51	3.457%	$233.3059	$233.31	$233.30	$233.30
Purchase #4	$218.35	6.221%	$231.9336	$231.93	$231.95	$231.90
Purchase #5	$73.78	12.202%	$82.7826	$82.78	$82.80	$82.80
Purchase #6	$53.63	9.735%	$58.8509	$58.85	$58.85	$58.90
Purchase #7	$143.99	13.211%	$163.0125	$163.01	$163.00	$163.00
7 purchase totals =	$815.50		$883.6510	$883.64	$883.65	$883.70