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	$250.79	5.470%	$264.5082	$264.51	$264.50	$264.50
Purchase #2	$216.63	8.412%	$234.8529	$234.85	$234.85	$234.90
Purchase #3	$144.60	7.789%	$155.8629	$155.86	$155.85	$155.90
Purchase #4	$153.97	12.673%	$173.4826	$173.48	$173.50	$173.50
Purchase #5	$250.70	4.768%	$262.6534	$262.65	$262.65	$262.70
Purchase #6	$66.26	9.383%	$72.4772	$72.48	$72.50	$72.50
Purchase #7	$114.84	7.861%	$123.8676	$123.87	$123.85	$123.90
7 purchase totals =	$1,197.79		$1,287.7048	$1,287.70	$1,287.70	$1,287.90