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	$248.70	4.684%	$260.3491	$260.35	$260.35	$260.30
Purchase #2	$90.84	13.840%	$103.4123	$103.41	$103.40	$103.40
Purchase #3	$127.52	5.758%	$134.8626	$134.86	$134.85	$134.90
Purchase #4	$72.72	3.367%	$75.1685	$75.17	$75.15	$75.20
Purchase #5	$12.60	13.697%	$14.3258	$14.33	$14.35	$14.30
Purchase #6	$217.83	9.678%	$238.9116	$238.91	$238.90	$238.90
Purchase #7	$195.72	8.587%	$212.5265	$212.53	$212.55	$212.50
7 purchase totals =	$965.93		$1,039.5564	$1,039.56	$1,039.55	$1,039.50