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	$73.29	5.150%	$77.0644	$77.06	$77.05	$77.10
Purchase #2	$121.50	10.822%	$134.6487	$134.65	$134.65	$134.60
Purchase #3	$191.95	4.141%	$199.8986	$199.90	$199.90	$199.90
Purchase #4	$184.98	13.645%	$210.2205	$210.22	$210.20	$210.20
Purchase #5	$145.57	3.676%	$150.9212	$150.92	$150.90	$150.90
Purchase #6	$51.50	9.509%	$56.3971	$56.40	$56.40	$56.40
Purchase #7	$187.88	11.718%	$209.8958	$209.90	$209.90	$209.90
7 purchase totals =	$956.67		$1,039.0463	$1,039.05	$1,039.00	$1,039.00