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	$16.35	12.623%	$18.4139	$18.41	$18.40	$18.40
Purchase #2	$209.55	12.111%	$234.9286	$234.93	$234.95	$234.90
Purchase #3	$236.91	9.799%	$260.1248	$260.12	$260.10	$260.10
Purchase #4	$184.66	6.426%	$196.5263	$196.53	$196.55	$196.50
Purchase #5	$196.78	5.353%	$207.3136	$207.31	$207.30	$207.30
Purchase #6	$76.93	10.635%	$85.1115	$85.11	$85.10	$85.10
Purchase #7	$77.89	3.475%	$80.5967	$80.60	$80.60	$80.60
7 purchase totals =	$999.07		$1,083.0154	$1,083.01	$1,083.00	$1,082.90