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	$229.42	11.730%	$256.331	$256.33	$256.35	$256.30
Purchase #2	$77.33	7.861%	$83.4089	$83.41	$83.40	$83.40
Purchase #3	$235.98	12.578%	$265.6616	$265.66	$265.65	$265.70
Purchase #4	$140.91	3.336%	$145.6108	$145.61	$145.60	$145.60
Purchase #5	$51.91	3.497%	$53.7253	$53.73	$53.75	$53.70
Purchase #6	$54.61	3.542%	$56.5443	$56.54	$56.55	$56.50
Purchase #7	$125.40	6.184%	$133.1547	$133.15	$133.15	$133.20
7 purchase totals =	$915.56		$994.4366	$994.43	$994.45	$994.40