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	$7.78	13.459%	$8.8271	$8.83	$8.85	$8.80
Purchase #2	$207.61	10.231%	$228.8506	$228.85	$228.85	$228.90
Purchase #3	$55.99	6.670%	$59.7245	$59.72	$59.70	$59.70
Purchase #4	$43.61	7.768%	$46.9976	$47.00	$47.00	$47.00
Purchase #5	$50.93	5.154%	$53.5549	$53.55	$53.55	$53.60
Purchase #6	$114.48	4.329%	$119.4358	$119.44	$119.45	$119.40
Purchase #7	$72.95	11.873%	$81.6114	$81.61	$81.60	$81.60
7 purchase totals =	$553.35		$599.0019	$599.00	$599.00	$599.00