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	$165.30	10.121%	$182.03	$182.03	$182.05	$182.00
Purchase #2	$44.72	8.368%	$48.4622	$48.46	$48.45	$48.50
Purchase #3	$247.30	6.441%	$263.2286	$263.23	$263.25	$263.20
Purchase #4	$139.92	13.444%	$158.7308	$158.73	$158.75	$158.70
Purchase #5	$50.29	8.345%	$54.4867	$54.49	$54.50	$54.50
Purchase #6	$111.46	4.130%	$116.0633	$116.06	$116.05	$116.10
Purchase #7	$32.30	6.835%	$34.5077	$34.51	$34.50	$34.50
7 purchase totals =	$791.29		$857.5093	$857.51	$857.55	$857.50