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	$139.92	3.642%	$145.0159	$145.02	$145.00	$145.00
Purchase #2	$224.50	6.516%	$239.1284	$239.13	$239.15	$239.10
Purchase #3	$224.87	9.600%	$246.4575	$246.46	$246.45	$246.50
Purchase #4	$59.72	13.154%	$67.5756	$67.58	$67.60	$67.60
Purchase #5	$12.91	5.552%	$13.6268	$13.63	$13.65	$13.60
Purchase #6	$59.85	13.418%	$67.8807	$67.88	$67.90	$67.90
Purchase #7	$57.72	5.523%	$60.9079	$60.91	$60.90	$60.90
7 purchase totals =	$779.49		$840.5928	$840.61	$840.65	$840.60