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	$138.94	3.179%	$143.3569	$143.36	$143.35	$143.40
Purchase #2	$182.54	4.868%	$191.426	$191.43	$191.45	$191.40
Purchase #3	$11.82	3.775%	$12.2662	$12.27	$12.25	$12.30
Purchase #4	$50.82	5.484%	$53.607	$53.61	$53.60	$53.60
Purchase #5	$59.79	13.463%	$67.8395	$67.84	$67.85	$67.80
Purchase #6	$122.79	13.188%	$138.9835	$138.98	$139.00	$139.00
Purchase #7	$189.61	4.842%	$198.7909	$198.79	$198.80	$198.80
7 purchase totals =	$756.31		$806.2700	$806.28	$806.30	$806.30