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	$242.58	6.429%	$258.1755	$258.18	$258.20	$258.20
Purchase #2	$69.71	12.737%	$78.589	$78.59	$78.60	$78.60
Purchase #3	$73.68	9.109%	$80.3915	$80.39	$80.40	$80.40
Purchase #4	$187.85	3.538%	$194.4961	$194.50	$194.50	$194.50
Purchase #5	$128.68	13.174%	$145.6323	$145.63	$145.65	$145.60
Purchase #6	$172.74	13.707%	$196.4175	$196.42	$196.40	$196.40
Purchase #7	$86.81	3.498%	$89.8466	$89.85	$89.85	$89.80
7 purchase totals =	$962.05		$1,043.5485	$1,043.56	$1,043.60	$1,043.50