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	$66.49	7.360%	$71.3837	$71.38	$71.40	$71.40
Purchase #2	$52.66	8.196%	$56.976	$56.98	$57.00	$57.00
Purchase #3	$164.40	7.405%	$176.5738	$176.57	$176.55	$176.60
Purchase #4	$231.65	9.725%	$254.178	$254.18	$254.20	$254.20
Purchase #5	$227.82	4.874%	$238.9239	$238.92	$238.90	$238.90
Purchase #6	$40.66	11.304%	$45.2562	$45.26	$45.25	$45.30
Purchase #7	$81.42	9.693%	$89.312	$89.31	$89.30	$89.30
7 purchase totals =	$865.10		$932.6036	$932.60	$932.60	$932.70