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	$159.81	5.323%	$168.3167	$168.32	$168.30	$168.30
Purchase #2	$67.91	6.683%	$72.4484	$72.45	$72.45	$72.40
Purchase #3	$211.63	13.377%	$239.9397	$239.94	$239.95	$239.90
Purchase #4	$141.49	13.296%	$160.3025	$160.30	$160.30	$160.30
Purchase #5	$184.68	7.641%	$198.7914	$198.79	$198.80	$198.80
Purchase #6	$165.61	7.778%	$178.4911	$178.49	$178.50	$178.50
Purchase #7	$34.36	9.383%	$37.584	$37.58	$37.60	$37.60
7 purchase totals =	$965.49		$1,055.8738	$1,055.87	$1,055.90	$1,055.80