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	$200.74	10.724%	$222.2674	$222.27	$222.25	$222.30
Purchase #2	$67.89	9.735%	$74.4991	$74.50	$74.50	$74.50
Purchase #3	$16.51	12.595%	$18.5894	$18.59	$18.60	$18.60
Purchase #4	$191.80	10.332%	$211.6168	$211.62	$211.60	$211.60
Purchase #5	$71.29	11.861%	$79.7457	$79.75	$79.75	$79.70
Purchase #6	$35.46	13.813%	$40.3581	$40.36	$40.35	$40.40
Purchase #7	$176.47	4.109%	$183.7212	$183.72	$183.70	$183.70
7 purchase totals =	$760.16		$830.7977	$830.81	$830.75	$830.80