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	$245.29	6.434%	$261.072	$261.07	$261.05	$261.10
Purchase #2	$239.88	11.496%	$267.4566	$267.46	$267.45	$267.50
Purchase #3	$215.89	10.797%	$239.1996	$239.20	$239.20	$239.20
Purchase #4	$60.30	10.139%	$66.4138	$66.41	$66.40	$66.40
Purchase #5	$41.81	9.818%	$45.9149	$45.91	$45.90	$45.90
Purchase #6	$49.89	10.697%	$55.2267	$55.23	$55.25	$55.20
Purchase #7	$101.87	3.645%	$105.5832	$105.58	$105.60	$105.60
7 purchase totals =	$954.93		$1,040.8668	$1,040.86	$1,040.85	$1,040.90