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	$155.71	5.556%	$164.3612	$164.36	$164.35	$164.40
Purchase #2	$235.65	8.641%	$256.0125	$256.01	$256.00	$256.00
Purchase #3	$177.49	13.209%	$200.9347	$200.93	$200.95	$200.90
Purchase #4	$163.78	10.113%	$180.3431	$180.34	$180.35	$180.30
Purchase #5	$77.81	13.514%	$88.3252	$88.33	$88.35	$88.30
Purchase #6	$145.94	8.597%	$158.4865	$158.49	$158.50	$158.50
Purchase #7	$127.79	11.708%	$142.7517	$142.75	$142.75	$142.80
7 purchase totals =	$1,084.17		$1,191.2149	$1,191.21	$1,191.25	$1,191.20