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	$39.66	9.387%	$43.3829	$43.38	$43.40	$43.40
Purchase #2	$169.35	6.275%	$179.9767	$179.98	$180.00	$180.00
Purchase #3	$56.72	4.558%	$59.3053	$59.31	$59.30	$59.30
Purchase #4	$29.48	3.757%	$30.5876	$30.59	$30.60	$30.60
Purchase #5	$167.69	7.293%	$179.9196	$179.92	$179.90	$179.90
Purchase #6	$200.91	9.791%	$220.5811	$220.58	$220.60	$220.60
Purchase #7	$123.62	5.301%	$130.1731	$130.17	$130.15	$130.20
7 purchase totals =	$787.43		$843.9263	$843.93	$843.95	$844.00