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	$71.38	13.128%	$80.7508	$80.75	$80.75	$80.80
Purchase #2	$72.71	8.134%	$78.6242	$78.62	$78.60	$78.60
Purchase #3	$178.83	3.363%	$184.8441	$184.84	$184.85	$184.80
Purchase #4	$86.78	4.648%	$90.8135	$90.81	$90.80	$90.80
Purchase #5	$169.90	7.717%	$183.0112	$183.01	$183.00	$183.00
Purchase #6	$149.96	7.594%	$161.348	$161.35	$161.35	$161.30
Purchase #7	$93.40	5.481%	$98.5193	$98.52	$98.50	$98.50
7 purchase totals =	$822.96		$877.9111	$877.90	$877.85	$877.80