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	$100.26	13.335%	$113.6297	$113.63	$113.65	$113.60
Purchase #2	$58.83	5.796%	$62.2398	$62.24	$62.25	$62.20
Purchase #3	$247.95	4.190%	$258.3391	$258.34	$258.35	$258.30
Purchase #4	$78.42	5.817%	$82.9817	$82.98	$83.00	$83.00
Purchase #5	$239.59	11.247%	$266.5367	$266.54	$266.55	$266.50
Purchase #6	$95.50	5.462%	$100.7162	$100.72	$100.70	$100.70
Purchase #7	$43.90	5.839%	$46.4633	$46.46	$46.45	$46.50
7 purchase totals =	$864.45		$930.9065	$930.91	$930.95	$930.80