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	$204.85	9.153%	$223.5999	$223.60	$223.60	$223.60
Purchase #2	$155.73	10.768%	$172.499	$172.50	$172.50	$172.50
Purchase #3	$176.89	13.293%	$200.404	$200.40	$200.40	$200.40
Purchase #4	$16.91	4.794%	$17.7207	$17.72	$17.70	$17.70
Purchase #5	$211.52	3.196%	$218.2802	$218.28	$218.30	$218.30
Purchase #6	$250.47	13.724%	$284.8445	$284.84	$284.85	$284.80
Purchase #7	$168.53	3.575%	$174.5549	$174.55	$174.55	$174.60
7 purchase totals =	$1,184.90		$1,291.9032	$1,291.89	$1,291.90	$1,291.90