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	$81.66	9.841%	$89.6962	$89.70	$89.70	$89.70
Purchase #2	$64.51	12.385%	$72.4996	$72.50	$72.50	$72.50
Purchase #3	$136.67	11.187%	$151.9593	$151.96	$151.95	$152.00
Purchase #4	$24.43	5.110%	$25.6784	$25.68	$25.70	$25.70
Purchase #5	$173.70	4.376%	$181.3011	$181.30	$181.30	$181.30
Purchase #6	$49.61	8.491%	$53.8224	$53.82	$53.80	$53.80
Purchase #7	$41.55	4.390%	$43.374	$43.37	$43.35	$43.40
7 purchase totals =	$572.13		$618.3310	$618.33	$618.30	$618.40