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	$11.40	10.540%	$12.6016	$12.60	$12.60	$12.60
Purchase #2	$22.71	12.473%	$25.5426	$25.54	$25.55	$25.50
Purchase #3	$183.52	4.439%	$191.6665	$191.67	$191.65	$191.70
Purchase #4	$147.67	13.105%	$167.0222	$167.02	$167.00	$167.00
Purchase #5	$241.89	6.478%	$257.5596	$257.56	$257.55	$257.60
Purchase #6	$16.57	7.778%	$17.8588	$17.86	$17.85	$17.90
Purchase #7	$82.36	8.537%	$89.3911	$89.39	$89.40	$89.40
7 purchase totals =	$706.12		$761.6424	$761.64	$761.60	$761.70