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	$124.50	5.849%	$131.782	$131.78	$131.80	$131.80
Purchase #2	$188.35	13.622%	$214.007	$214.01	$214.00	$214.00
Purchase #3	$247.80	4.211%	$258.2349	$258.23	$258.25	$258.20
Purchase #4	$48.29	10.403%	$53.3136	$53.31	$53.30	$53.30
Purchase #5	$93.31	6.324%	$99.2109	$99.21	$99.20	$99.20
Purchase #6	$103.32	7.284%	$110.8458	$110.85	$110.85	$110.80
Purchase #7	$95.53	8.329%	$103.4867	$103.49	$103.50	$103.50
7 purchase totals =	$901.10		$970.8809	$970.88	$970.90	$970.80