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	$172.48	3.245%	$178.077	$178.08	$178.10	$178.10
Purchase #2	$90.31	4.505%	$94.3785	$94.38	$94.40	$94.40
Purchase #3	$184.77	3.704%	$191.6139	$191.61	$191.60	$191.60
Purchase #4	$233.93	13.414%	$265.3094	$265.31	$265.30	$265.30
Purchase #5	$157.45	13.542%	$178.7719	$178.77	$178.75	$178.80
Purchase #6	$141.82	9.396%	$155.1454	$155.15	$155.15	$155.10
Purchase #7	$250.90	9.440%	$274.585	$274.59	$274.60	$274.60
7 purchase totals =	$1,231.66		$1,337.8811	$1,337.89	$1,337.90	$1,337.90