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	$165.83	9.462%	$181.5208	$181.52	$181.50	$181.50
Purchase #2	$121.25	10.633%	$134.1425	$134.14	$134.15	$134.10
Purchase #3	$74.87	5.362%	$78.8845	$78.88	$78.90	$78.90
Purchase #4	$155.45	6.734%	$165.918	$165.92	$165.90	$165.90
Purchase #5	$42.84	5.755%	$45.3054	$45.31	$45.30	$45.30
Purchase #6	$7.65	9.389%	$8.3683	$8.37	$8.35	$8.40
Purchase #7	$23.66	7.283%	$25.3832	$25.38	$25.40	$25.40
7 purchase totals =	$591.55		$639.5227	$639.52	$639.50	$639.50