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	$33.42	11.754%	$37.3482	$37.35	$37.35	$37.30
Purchase #2	$21.70	12.678%	$24.4511	$24.45	$24.45	$24.50
Purchase #3	$11.67	10.230%	$12.8638	$12.86	$12.85	$12.90
Purchase #4	$56.54	4.325%	$58.9854	$58.99	$59.00	$59.00
Purchase #5	$30.27	9.817%	$33.2416	$33.24	$33.25	$33.20
Purchase #6	$94.63	8.137%	$102.33	$102.33	$102.35	$102.30
Purchase #7	$82.48	4.789%	$86.43	$86.43	$86.45	$86.40
7 purchase totals =	$330.71		$355.6501	$355.65	$355.70	$355.60