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	$176.87	5.651%	$186.8649	$186.86	$186.85	$186.90
Purchase #2	$250.88	11.812%	$280.5139	$280.51	$280.50	$280.50
Purchase #3	$52.83	7.469%	$56.7759	$56.78	$56.80	$56.80
Purchase #4	$13.89	9.553%	$15.2169	$15.22	$15.20	$15.20
Purchase #5	$46.40	8.584%	$50.383	$50.38	$50.40	$50.40
Purchase #6	$30.77	12.813%	$34.7126	$34.71	$34.70	$34.70
Purchase #7	$133.44	9.330%	$145.89	$145.89	$145.90	$145.90
7 purchase totals =	$705.08		$770.3572	$770.35	$770.35	$770.40