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	$233.39	3.333%	$241.1689	$241.17	$241.15	$241.20
Purchase #2	$106.37	6.354%	$113.1287	$113.13	$113.15	$113.10
Purchase #3	$105.53	5.668%	$111.5114	$111.51	$111.50	$111.50
Purchase #4	$55.72	11.334%	$62.0353	$62.04	$62.05	$62.00
Purchase #5	$238.33	10.296%	$262.8685	$262.87	$262.85	$262.90
Purchase #6	$59.25	12.608%	$66.7202	$66.72	$66.70	$66.70
Purchase #7	$55.87	10.173%	$61.5537	$61.55	$61.55	$61.60
7 purchase totals =	$854.46		$918.9867	$918.99	$918.95	$919.00