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	$56.72	12.261%	$63.6744	$63.67	$63.65	$63.70
Purchase #2	$172.99	4.478%	$180.7365	$180.74	$180.75	$180.70
Purchase #3	$21.51	12.397%	$24.1766	$24.18	$24.20	$24.20
Purchase #4	$76.72	12.680%	$86.4481	$86.45	$86.45	$86.40
Purchase #5	$206.31	12.201%	$231.4819	$231.48	$231.50	$231.50
Purchase #6	$38.92	11.357%	$43.3401	$43.34	$43.35	$43.30
Purchase #7	$86.84	3.597%	$89.9636	$89.96	$89.95	$90.00
7 purchase totals =	$660.01		$719.8212	$719.82	$719.85	$719.80