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	$37.77	6.289%	$40.1454	$40.15	$40.15	$40.10
Purchase #2	$19.47	12.269%	$21.8588	$21.86	$21.85	$21.90
Purchase #3	$85.76	8.754%	$93.2674	$93.27	$93.25	$93.30
Purchase #4	$192.40	4.271%	$200.6174	$200.62	$200.60	$200.60
Purchase #5	$212.43	6.676%	$226.6118	$226.61	$226.60	$226.60
Purchase #6	$94.68	4.711%	$99.1404	$99.14	$99.15	$99.10
Purchase #7	$131.37	8.566%	$142.6232	$142.62	$142.60	$142.60
7 purchase totals =	$773.88		$824.2644	$824.27	$824.20	$824.20