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	$34.78	11.667%	$38.8378	$38.84	$38.85	$38.80
Purchase #2	$40.61	11.565%	$45.3065	$45.31	$45.30	$45.30
Purchase #3	$228.77	6.608%	$243.8871	$243.89	$243.90	$243.90
Purchase #4	$54.88	8.711%	$59.6606	$59.66	$59.65	$59.70
Purchase #5	$143.71	9.126%	$156.825	$156.83	$156.85	$156.80
Purchase #6	$163.60	8.460%	$177.4406	$177.44	$177.45	$177.40
Purchase #7	$94.28	6.717%	$100.6128	$100.61	$100.60	$100.60
7 purchase totals =	$760.63		$822.5704	$822.58	$822.60	$822.50