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	$27.79	4.325%	$28.9919	$28.99	$29.00	$29.00
Purchase #2	$54.78	8.799%	$59.6001	$59.60	$59.60	$59.60
Purchase #3	$59.70	8.355%	$64.6879	$64.69	$64.70	$64.70
Purchase #4	$12.40	4.472%	$12.9545	$12.95	$12.95	$13.00
Purchase #5	$139.49	7.233%	$149.5793	$149.58	$149.60	$149.60
Purchase #6	$88.27	13.480%	$100.1688	$100.17	$100.15	$100.20
Purchase #7	$205.89	7.769%	$221.8856	$221.89	$221.90	$221.90
7 purchase totals =	$588.32		$637.8681	$637.87	$637.90	$638.00