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	$150.89	8.742%	$164.0808	$164.08	$164.10	$164.10
Purchase #2	$25.45	13.242%	$28.8201	$28.82	$28.80	$28.80
Purchase #3	$141.61	13.451%	$160.658	$160.66	$160.65	$160.70
Purchase #4	$11.75	9.773%	$12.8983	$12.90	$12.90	$12.90
Purchase #5	$10.41	9.812%	$11.4314	$11.43	$11.45	$11.40
Purchase #6	$113.28	4.123%	$117.9505	$117.95	$117.95	$118.00
Purchase #7	$40.41	6.349%	$42.9756	$42.98	$43.00	$43.00
7 purchase totals =	$493.80		$538.8147	$538.82	$538.85	$538.90