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	$176.87	4.872%	$185.4871	$185.49	$185.50	$185.50
Purchase #2	$154.56	6.401%	$164.4534	$164.45	$164.45	$164.50
Purchase #3	$49.63	3.161%	$51.1988	$51.20	$51.20	$51.20
Purchase #4	$168.99	6.230%	$179.5181	$179.52	$179.50	$179.50
Purchase #5	$237.88	13.299%	$269.5157	$269.52	$269.50	$269.50
Purchase #6	$133.81	3.713%	$138.7784	$138.78	$138.80	$138.80
Purchase #7	$108.62	12.410%	$122.0997	$122.10	$122.10	$122.10
7 purchase totals =	$1,030.36		$1,111.0512	$1,111.06	$1,111.05	$1,111.10