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	$239.57	6.140%	$254.2796	$254.28	$254.30	$254.30
Purchase #2	$112.53	3.786%	$116.7904	$116.79	$116.80	$116.80
Purchase #3	$92.93	12.247%	$104.3111	$104.31	$104.30	$104.30
Purchase #4	$95.36	6.457%	$101.5174	$101.52	$101.50	$101.50
Purchase #5	$101.43	4.786%	$106.2844	$106.28	$106.30	$106.30
Purchase #6	$25.96	6.123%	$27.5495	$27.55	$27.55	$27.50
Purchase #7	$96.85	9.309%	$105.8658	$105.87	$105.85	$105.90
7 purchase totals =	$764.63		$816.5982	$816.60	$816.60	$816.60