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	$7.31	6.376%	$7.7761	$7.78	$7.80	$7.80
Purchase #2	$134.67	12.445%	$151.4297	$151.43	$151.45	$151.40
Purchase #3	$206.59	10.434%	$228.1456	$228.15	$228.15	$228.10
Purchase #4	$108.31	3.328%	$111.9146	$111.91	$111.90	$111.90
Purchase #5	$75.89	4.233%	$79.1024	$79.10	$79.10	$79.10
Purchase #6	$224.39	3.253%	$231.6894	$231.69	$231.70	$231.70
Purchase #7	$125.68	4.197%	$130.9548	$130.95	$130.95	$131.00
7 purchase totals =	$882.84		$941.0126	$941.01	$941.05	$941.00