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	$11.90	6.667%	$12.6934	$12.69	$12.70	$12.70
Purchase #2	$55.46	6.391%	$59.0044	$59.00	$59.00	$59.00
Purchase #3	$174.91	9.260%	$191.1067	$191.11	$191.10	$191.10
Purchase #4	$206.91	3.608%	$214.3753	$214.38	$214.40	$214.40
Purchase #5	$48.92	13.411%	$55.4807	$55.48	$55.50	$55.50
Purchase #6	$75.90	12.771%	$85.5932	$85.59	$85.60	$85.60
Purchase #7	$40.61	5.263%	$42.7473	$42.75	$42.75	$42.70
7 purchase totals =	$614.61		$661.0010	$661.00	$661.05	$661.00