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	$201.96	9.694%	$221.538	$221.54	$221.55	$221.50
Purchase #2	$157.76	11.196%	$175.4228	$175.42	$175.40	$175.40
Purchase #3	$55.44	7.242%	$59.455	$59.46	$59.45	$59.50
Purchase #4	$242.61	3.455%	$250.9922	$250.99	$251.00	$251.00
Purchase #5	$6.80	10.874%	$7.5394	$7.54	$7.55	$7.50
Purchase #6	$133.46	7.274%	$143.1679	$143.17	$143.15	$143.20
Purchase #7	$117.36	13.743%	$133.4888	$133.49	$133.50	$133.50
7 purchase totals =	$915.39		$991.6041	$991.61	$991.60	$991.60