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	$96.82	3.589%	$100.2949	$100.29	$100.30	$100.30
Purchase #2	$241.92	5.459%	$255.1264	$255.13	$255.15	$255.10
Purchase #3	$177.30	8.863%	$193.0141	$193.01	$193.00	$193.00
Purchase #4	$204.79	7.567%	$220.2865	$220.29	$220.30	$220.30
Purchase #5	$102.27	9.746%	$112.2372	$112.24	$112.25	$112.20
Purchase #6	$82.28	9.845%	$90.3805	$90.38	$90.40	$90.40
Purchase #7	$218.73	9.372%	$239.2294	$239.23	$239.25	$239.20
7 purchase totals =	$1,124.11		$1,210.5690	$1,210.57	$1,210.65	$1,210.50