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	$89.40	12.362%	$100.4516	$100.45	$100.45	$100.50
Purchase #2	$239.77	3.342%	$247.7831	$247.78	$247.80	$247.80
Purchase #3	$145.99	3.302%	$150.8106	$150.81	$150.80	$150.80
Purchase #4	$164.99	9.115%	$180.0288	$180.03	$180.05	$180.00
Purchase #5	$144.76	11.535%	$161.4581	$161.46	$161.45	$161.50
Purchase #6	$138.50	7.156%	$148.4111	$148.41	$148.40	$148.40
Purchase #7	$154.81	13.214%	$175.2666	$175.27	$175.25	$175.30
7 purchase totals =	$1,078.22		$1,164.2099	$1,164.21	$1,164.20	$1,164.30