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	$235.84	9.823%	$259.0066	$259.01	$259.00	$259.00
Purchase #2	$115.58	7.394%	$124.126	$124.13	$124.15	$124.10
Purchase #3	$136.81	7.365%	$146.8861	$146.89	$146.90	$146.90
Purchase #4	$59.53	3.218%	$61.4457	$61.45	$61.45	$61.40
Purchase #5	$179.51	11.771%	$200.6401	$200.64	$200.65	$200.60
Purchase #6	$34.41	11.109%	$38.2326	$38.23	$38.25	$38.20
Purchase #7	$60.76	4.300%	$63.3727	$63.37	$63.35	$63.40
7 purchase totals =	$822.44		$893.7098	$893.72	$893.75	$893.60