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	$171.60	3.440%	$177.503	$177.50	$177.50	$177.50
Purchase #2	$127.45	11.187%	$141.7078	$141.71	$141.70	$141.70
Purchase #3	$204.33	13.348%	$231.604	$231.60	$231.60	$231.60
Purchase #4	$31.42	5.529%	$33.1572	$33.16	$33.15	$33.20
Purchase #5	$113.52	13.547%	$128.8986	$128.90	$128.90	$128.90
Purchase #6	$46.49	12.707%	$52.3975	$52.40	$52.40	$52.40
Purchase #7	$106.96	12.683%	$120.5257	$120.53	$120.55	$120.50
7 purchase totals =	$801.77		$885.7938	$885.80	$885.80	$885.80