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	$168.88	6.780%	$180.3301	$180.33	$180.35	$180.30
Purchase #2	$60.57	11.473%	$67.5192	$67.52	$67.50	$67.50
Purchase #3	$116.41	8.725%	$126.5668	$126.57	$126.55	$126.60
Purchase #4	$38.98	3.422%	$40.3139	$40.31	$40.30	$40.30
Purchase #5	$234.75	8.443%	$254.5699	$254.57	$254.55	$254.60
Purchase #6	$247.44	12.482%	$278.3255	$278.33	$278.35	$278.30
Purchase #7	$245.34	5.164%	$258.0094	$258.01	$258.00	$258.00
7 purchase totals =	$1,112.37		$1,205.6348	$1,205.64	$1,205.60	$1,205.60