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	$179.71	6.392%	$191.1971	$191.20	$191.20	$191.20
Purchase #2	$92.25	4.148%	$96.0765	$96.08	$96.10	$96.10
Purchase #3	$131.34	9.509%	$143.8291	$143.83	$143.85	$143.80
Purchase #4	$114.35	7.571%	$123.0074	$123.01	$123.00	$123.00
Purchase #5	$149.40	7.405%	$160.4631	$160.46	$160.45	$160.50
Purchase #6	$23.68	3.506%	$24.5102	$24.51	$24.50	$24.50
Purchase #7	$96.36	7.687%	$103.7672	$103.77	$103.75	$103.80
7 purchase totals =	$787.09		$842.8506	$842.86	$842.85	$842.90