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	$100.90	6.519%	$107.4777	$107.48	$107.50	$107.50
Purchase #2	$95.29	3.314%	$98.4479	$98.45	$98.45	$98.40
Purchase #3	$89.75	6.273%	$95.38	$95.38	$95.40	$95.40
Purchase #4	$205.56	4.724%	$215.2707	$215.27	$215.25	$215.30
Purchase #5	$19.33	8.331%	$20.9404	$20.94	$20.95	$20.90
Purchase #6	$46.53	7.199%	$49.8797	$49.88	$49.90	$49.90
Purchase #7	$50.43	5.289%	$53.0972	$53.10	$53.10	$53.10
7 purchase totals =	$607.79		$640.4936	$640.50	$640.55	$640.50