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	$56.26	5.346%	$59.2677	$59.27	$59.25	$59.30
Purchase #2	$225.85	13.367%	$256.0394	$256.04	$256.05	$256.00
Purchase #3	$11.27	9.631%	$12.3554	$12.36	$12.35	$12.40
Purchase #4	$81.51	12.238%	$91.4852	$91.49	$91.50	$91.50
Purchase #5	$18.44	7.667%	$19.8538	$19.85	$19.85	$19.90
Purchase #6	$132.85	3.545%	$137.5595	$137.56	$137.55	$137.60
Purchase #7	$59.31	12.698%	$66.8412	$66.84	$66.85	$66.80
7 purchase totals =	$585.49		$643.4022	$643.41	$643.40	$643.50