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	$117.66	8.215%	$127.3258	$127.33	$127.35	$127.30
Purchase #2	$240.57	10.588%	$266.0416	$266.04	$266.05	$266.00
Purchase #3	$242.78	4.155%	$252.8675	$252.87	$252.85	$252.90
Purchase #4	$12.89	4.851%	$13.5153	$13.52	$13.50	$13.50
Purchase #5	$118.97	3.590%	$123.241	$123.24	$123.25	$123.20
Purchase #6	$241.81	3.659%	$250.6578	$250.66	$250.65	$250.70
Purchase #7	$231.55	10.348%	$255.5108	$255.51	$255.50	$255.50
7 purchase totals =	$1,206.23		$1,289.1598	$1,289.17	$1,289.15	$1,289.10