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	$16.33	13.868%	$18.5946	$18.59	$18.60	$18.60
Purchase #2	$240.74	6.422%	$256.2003	$256.20	$256.20	$256.20
Purchase #3	$140.27	12.156%	$157.3212	$157.32	$157.30	$157.30
Purchase #4	$81.33	6.527%	$86.6384	$86.64	$86.65	$86.60
Purchase #5	$180.85	10.850%	$200.4722	$200.47	$200.45	$200.50
Purchase #6	$240.34	11.550%	$268.0993	$268.10	$268.10	$268.10
Purchase #7	$45.78	13.589%	$52.001	$52.00	$52.00	$52.00
7 purchase totals =	$945.64		$1,039.3270	$1,039.32	$1,039.30	$1,039.30