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	$40.43	13.538%	$45.9034	$45.90	$45.90	$45.90
Purchase #2	$135.96	5.248%	$143.0952	$143.10	$143.10	$143.10
Purchase #3	$243.55	5.493%	$256.9282	$256.93	$256.95	$256.90
Purchase #4	$123.94	3.636%	$128.4465	$128.45	$128.45	$128.40
Purchase #5	$49.92	3.436%	$51.6353	$51.64	$51.65	$51.60
Purchase #6	$49.72	10.325%	$54.8536	$54.85	$54.85	$54.90
Purchase #7	$148.93	6.410%	$158.4764	$158.48	$158.50	$158.50
7 purchase totals =	$792.45		$839.3386	$839.35	$839.40	$839.30