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	$250.34	11.589%	$279.3519	$279.35	$279.35	$279.40
Purchase #2	$83.86	8.154%	$90.6979	$90.70	$90.70	$90.70
Purchase #3	$227.50	5.320%	$239.603	$239.60	$239.60	$239.60
Purchase #4	$156.52	12.705%	$176.4059	$176.41	$176.40	$176.40
Purchase #5	$117.92	13.333%	$133.6423	$133.64	$133.65	$133.60
Purchase #6	$10.90	12.551%	$12.2681	$12.27	$12.25	$12.30
Purchase #7	$162.60	4.507%	$169.9284	$169.93	$169.95	$169.90
7 purchase totals =	$1,009.64		$1,101.8975	$1,101.90	$1,101.90	$1,101.90