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	$121.58	5.583%	$128.3678	$128.37	$128.35	$128.40
Purchase #2	$207.87	7.442%	$223.3397	$223.34	$223.35	$223.30
Purchase #3	$186.86	13.193%	$211.5124	$211.51	$211.50	$211.50
Purchase #4	$22.53	12.530%	$25.353	$25.35	$25.35	$25.40
Purchase #5	$112.85	5.685%	$119.2655	$119.27	$119.25	$119.30
Purchase #6	$115.82	9.796%	$127.1657	$127.17	$127.15	$127.20
Purchase #7	$224.67	6.603%	$239.505	$239.51	$239.50	$239.50
7 purchase totals =	$992.18		$1,074.5091	$1,074.52	$1,074.45	$1,074.60