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	$13.59	11.556%	$15.1605	$15.16	$15.15	$15.20
Purchase #2	$112.58	10.115%	$123.9675	$123.97	$123.95	$124.00
Purchase #3	$111.55	13.414%	$126.5133	$126.51	$126.50	$126.50
Purchase #4	$82.86	10.646%	$91.6813	$91.68	$91.70	$91.70
Purchase #5	$125.59	10.751%	$139.0922	$139.09	$139.10	$139.10
Purchase #6	$233.57	6.715%	$249.2542	$249.25	$249.25	$249.30
Purchase #7	$117.89	11.686%	$131.6666	$131.67	$131.65	$131.70
7 purchase totals =	$797.63		$877.3356	$877.33	$877.30	$877.50