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	$242.40	13.296%	$274.6295	$274.63	$274.65	$274.60
Purchase #2	$77.59	11.404%	$86.4384	$86.44	$86.45	$86.40
Purchase #3	$50.78	3.259%	$52.4349	$52.43	$52.45	$52.40
Purchase #4	$129.64	11.711%	$144.8221	$144.82	$144.80	$144.80
Purchase #5	$220.41	6.816%	$235.4331	$235.43	$235.45	$235.40
Purchase #6	$77.94	9.246%	$85.1463	$85.15	$85.15	$85.10
Purchase #7	$228.71	10.514%	$252.7566	$252.76	$252.75	$252.80
7 purchase totals =	$1,027.47		$1,131.6609	$1,131.66	$1,131.70	$1,131.50