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	$12.73	7.174%	$13.6433	$13.64	$13.65	$13.60
Purchase #2	$236.60	3.824%	$245.6476	$245.65	$245.65	$245.60
Purchase #3	$64.69	11.212%	$71.943	$71.94	$71.95	$71.90
Purchase #4	$86.75	10.465%	$95.8284	$95.83	$95.85	$95.80
Purchase #5	$236.50	8.105%	$255.6683	$255.67	$255.65	$255.70
Purchase #6	$28.46	9.374%	$31.1278	$31.13	$31.15	$31.10
Purchase #7	$32.35	3.162%	$33.3729	$33.37	$33.35	$33.40
7 purchase totals =	$698.08		$747.2313	$747.23	$747.25	$747.10