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	$231.64	12.195%	$259.8885	$259.89	$259.90	$259.90
Purchase #2	$6.86	11.227%	$7.6302	$7.63	$7.65	$7.60
Purchase #3	$74.59	9.508%	$81.682	$81.68	$81.70	$81.70
Purchase #4	$6.86	7.632%	$7.3836	$7.38	$7.40	$7.40
Purchase #5	$209.94	6.673%	$223.9493	$223.95	$223.95	$223.90
Purchase #6	$200.29	13.609%	$227.5475	$227.55	$227.55	$227.50
Purchase #7	$141.85	4.669%	$148.473	$148.47	$148.45	$148.50
7 purchase totals =	$872.03		$956.5541	$956.55	$956.60	$956.50