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	$16.32	10.667%	$18.0609	$18.06	$18.05	$18.10
Purchase #2	$114.52	7.826%	$123.4823	$123.48	$123.50	$123.50
Purchase #3	$39.65	3.165%	$40.9049	$40.90	$40.90	$40.90
Purchase #4	$190.66	7.380%	$204.7307	$204.73	$204.75	$204.70
Purchase #5	$101.32	8.659%	$110.0933	$110.09	$110.10	$110.10
Purchase #6	$59.45	11.724%	$66.4199	$66.42	$66.40	$66.40
Purchase #7	$223.65	5.306%	$235.5169	$235.52	$235.50	$235.50
7 purchase totals =	$745.57		$799.2089	$799.20	$799.20	$799.20