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	$78.59	5.204%	$82.6798	$82.68	$82.70	$82.70
Purchase #2	$241.98	9.588%	$265.181	$265.18	$265.20	$265.20
Purchase #3	$134.98	12.735%	$152.1697	$152.17	$152.15	$152.20
Purchase #4	$37.80	12.160%	$42.3965	$42.40	$42.40	$42.40
Purchase #5	$56.68	3.228%	$58.5096	$58.51	$58.50	$58.50
Purchase #6	$107.92	10.438%	$119.1847	$119.18	$119.20	$119.20
Purchase #7	$86.93	4.471%	$90.8166	$90.82	$90.80	$90.80
7 purchase totals =	$744.88		$810.9379	$810.94	$810.95	$811.00