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	$119.90	6.381%	$127.5508	$127.55	$127.55	$127.60
Purchase #2	$246.92	13.827%	$281.0616	$281.06	$281.05	$281.10
Purchase #3	$10.74	10.517%	$11.8695	$11.87	$11.85	$11.90
Purchase #4	$215.93	10.395%	$238.3759	$238.38	$238.40	$238.40
Purchase #5	$52.57	6.299%	$55.8814	$55.88	$55.90	$55.90
Purchase #6	$46.87	9.337%	$51.2463	$51.25	$51.25	$51.20
Purchase #7	$74.35	5.333%	$78.3151	$78.32	$78.30	$78.30
7 purchase totals =	$767.28		$844.3006	$844.31	$844.30	$844.40