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	$52.75	5.277%	$55.5336	$55.53	$55.55	$55.50
Purchase #2	$35.54	13.832%	$40.4559	$40.46	$40.45	$40.50
Purchase #3	$142.81	8.708%	$155.2459	$155.25	$155.25	$155.20
Purchase #4	$205.74	5.208%	$216.4549	$216.45	$216.45	$216.50
Purchase #5	$245.84	10.474%	$271.5893	$271.59	$271.60	$271.60
Purchase #6	$38.31	4.362%	$39.9811	$39.98	$40.00	$40.00
Purchase #7	$239.30	9.702%	$262.5169	$262.52	$262.50	$262.50
7 purchase totals =	$960.29		$1,041.7776	$1,041.78	$1,041.80	$1,041.80