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	$226.89	6.591%	$241.8443	$241.84	$241.85	$241.80
Purchase #2	$201.29	3.741%	$208.8203	$208.82	$208.80	$208.80
Purchase #3	$133.53	7.826%	$143.9801	$143.98	$144.00	$144.00
Purchase #4	$50.74	8.178%	$54.8895	$54.89	$54.90	$54.90
Purchase #5	$111.87	7.107%	$119.8206	$119.82	$119.80	$119.80
Purchase #6	$60.75	10.305%	$67.0103	$67.01	$67.00	$67.00
Purchase #7	$149.54	4.358%	$156.057	$156.06	$156.05	$156.10
7 purchase totals =	$934.61		$992.4221	$992.42	$992.40	$992.40