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	$179.27	4.561%	$187.4465	$187.45	$187.45	$187.40
Purchase #2	$83.33	13.153%	$94.2904	$94.29	$94.30	$94.30
Purchase #3	$230.63	10.770%	$255.4689	$255.47	$255.45	$255.50
Purchase #4	$175.86	10.147%	$193.7045	$193.70	$193.70	$193.70
Purchase #5	$70.47	11.390%	$78.4965	$78.50	$78.50	$78.50
Purchase #6	$13.39	10.853%	$14.8432	$14.84	$14.85	$14.80
Purchase #7	$242.88	9.665%	$266.3544	$266.35	$266.35	$266.40
7 purchase totals =	$995.83		$1,090.6044	$1,090.60	$1,090.60	$1,090.60