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	$199.43	13.384%	$226.1217	$226.12	$226.10	$226.10
Purchase #2	$38.36	5.374%	$40.4215	$40.42	$40.40	$40.40
Purchase #3	$113.44	8.300%	$122.8555	$122.86	$122.85	$122.90
Purchase #4	$238.56	9.223%	$260.5624	$260.56	$260.55	$260.60
Purchase #5	$127.36	13.181%	$144.1473	$144.15	$144.15	$144.10
Purchase #6	$178.45	10.145%	$196.5538	$196.55	$196.55	$196.60
Purchase #7	$134.90	4.273%	$140.6643	$140.66	$140.65	$140.70
7 purchase totals =	$1,030.50		$1,131.3265	$1,131.32	$1,131.25	$1,131.40