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	$26.76	10.521%	$29.5754	$29.58	$29.60	$29.60
Purchase #2	$39.42	11.371%	$43.9024	$43.90	$43.90	$43.90
Purchase #3	$44.84	5.161%	$47.1542	$47.15	$47.15	$47.20
Purchase #4	$230.98	11.426%	$257.3718	$257.37	$257.35	$257.40
Purchase #5	$25.46	9.665%	$27.9207	$27.92	$27.90	$27.90
Purchase #6	$134.97	12.234%	$151.4822	$151.48	$151.50	$151.50
Purchase #7	$98.31	10.764%	$108.8921	$108.89	$108.90	$108.90
7 purchase totals =	$600.74		$666.2988	$666.29	$666.30	$666.40