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	$239.40	12.192%	$268.5876	$268.59	$268.60	$268.60
Purchase #2	$135.60	6.390%	$144.2648	$144.26	$144.25	$144.30
Purchase #3	$114.72	3.637%	$118.8924	$118.89	$118.90	$118.90
Purchase #4	$129.49	12.157%	$145.2321	$145.23	$145.25	$145.20
Purchase #5	$183.69	3.333%	$189.8124	$189.81	$189.80	$189.80
Purchase #6	$181.69	10.268%	$200.3459	$200.35	$200.35	$200.30
Purchase #7	$10.69	10.531%	$11.8158	$11.82	$11.80	$11.80
7 purchase totals =	$995.28		$1,078.9510	$1,078.95	$1,078.95	$1,078.90