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	$108.52	6.773%	$115.8701	$115.87	$115.85	$115.90
Purchase #2	$55.89	6.456%	$59.4983	$59.50	$59.50	$59.50
Purchase #3	$167.35	11.403%	$186.4329	$186.43	$186.45	$186.40
Purchase #4	$185.67	8.427%	$201.3164	$201.32	$201.30	$201.30
Purchase #5	$25.59	6.171%	$27.1692	$27.17	$27.15	$27.20
Purchase #6	$97.56	3.490%	$100.9648	$100.96	$100.95	$101.00
Purchase #7	$235.83	12.731%	$265.8535	$265.85	$265.85	$265.90
7 purchase totals =	$876.41		$957.1052	$957.10	$957.05	$957.20