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	$209.35	4.338%	$218.4316	$218.43	$218.45	$218.40
Purchase #2	$128.30	8.760%	$139.5391	$139.54	$139.55	$139.50
Purchase #3	$114.43	11.500%	$127.5895	$127.59	$127.60	$127.60
Purchase #4	$89.31	5.351%	$94.089	$94.09	$94.10	$94.10
Purchase #5	$200.99	5.139%	$211.3189	$211.32	$211.30	$211.30
Purchase #6	$163.30	13.509%	$185.3602	$185.36	$185.35	$185.40
Purchase #7	$150.26	8.847%	$163.5535	$163.55	$163.55	$163.60
7 purchase totals =	$1,055.94		$1,139.8818	$1,139.88	$1,139.90	$1,139.90